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[[Parliament of the United Kingdom|Parliamentary]] [[by-election]]s in the [[United Kingdom]] occur when a [[Member of Parliament (United Kingdom)|Member of Parliament]] (MP) vacates a [[House of Commons of the United Kingdom|House of Commons]] seat (due to [[Resignation from the House of Commons of the United Kingdom|resignation]], death, disqualification or expulsion) during the course of a parliament.

== Scope of these records ==
Although the history of Parliament is much older, most of these records concern only the period since [[1945 United Kingdom general election|1945]]. Earlier exceptional results are listed separately.

Parliaments of [[Parliament of England|England]], [[Parliament of Scotland|Scotland]], [[Parliament of Ireland|Ireland]] and the various unions of these Kingdoms had been assembled since the medieval period, though these bodies only gradually evolved to be democratically elected by the populace and records are incomplete. England and Wales had numerous "[[Rotten and pocket boroughs|rotten boroughs]]" with tiny and tightly controlled electorates until the [[Reform Act of 1832]]. The most recent significant expansions of the electoral franchise were the [[Representation of the People Act 1918]] which allowed some women to vote for the first time and greatly expanded the franchise of men, overall more than doubling the size of the electorate, and the [[Representation of the People (Equal Franchise) Act 1928]] which expanded the franchise of women to be equal to that of men.

Furthermore, there are various additional factors complicating comparisons between earlier results and modern cases. Among the most significant aspects of historical elections which are no longer present are:

*Frequent interventions and withdrawals of parties in different seats.
*Frequent coalitions between parties, splits within parties and floor-crossing by members.
*[[Uncontested election]]s and truces between parties, in particular during both World Wars.
*Generally more significant competition from independent candidates and minor parties.
*[[Multi-member constituencies in the Parliament of the United Kingdom|Multi-member seats]] and [[University constituency|university seats]] (abolished 1950).
*Higher frequency of by-elections, partly due to the practice of often uncontested [[Ministerial by-elections in the UK|ministerial by-elections]] which ended in 1926.
*Generally higher turnouts, although several wartime elections exhibited the lowest recorded turnouts.
*Generally higher variation in size of constituency electorates.

Since 1945, the legal and general political situation regarding by-elections has been broadly stable, allowing for meaningful comparison of records.

These records include those from [[Northern Ireland]]. However, the politics of Northern Ireland is mostly separate from that of Great Britain so comparisons can be problematic.

==Glossary==
For comparison purposes the following definitions have been adopted.

*'''Gain''' - victory by a party that was not victorious at the immediate previous election
*'''Loss''' - defeat of a party that was victorious at the immediate previous election
*'''Hold''' - victory by a party that was victorious at the immediate previous election
*'''Win''' - victory by a party. ambiguous term that could mean either a gain or a hold 
*'''Incumbent''' - the party that held the seat at the immediately previous election, irrespective of any intervening change of candidate or candidate's change of party
*'''Third party''' - In England, since [[1922 United Kingdom general election|1922]], the "third party" has been the [[Liberal Party (UK)|Liberal Party]] and its successor, the [[Liberal Democrats (UK)|Liberal Democrats]]. Additionally, in [[Scotland]] and [[Wales]] the [[Scottish National Party]] (SNP) and [[Plaid Cymru]] are also considered to be third parties. Prior to 1922, the third party was the [[Labour Party (UK)|Labour Party]].
*'''Minor party''' - parties smaller than the third party
*'''Uncontested''' - an election where only one candidate is put forward. No votes are actually cast and the candidate is by definition the victor.

==Numerical records==

For more information about what is meant by the term "swing", see [[Swing (United Kingdom)]]

===Largest swings in percentage share of votes===

{|class="wikitable sortable"
|-
!Election
!Swing
!colspan=2|From
!colspan=2|To
|-
|[[1983 Bermondsey by-election]]
|44.2
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Liberal Party (UK)))
|-
|[[2014 Clacton by-election]]
|44.1((efn|group=swing|name=incmp|Seat was held by the incumbent MP.))
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|UK Independence Party))
|-
|[[1973 Lincoln by-election]]
|43.0((efn|group=swing|name=incmp))
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Democratic Labour Party (UK, 1972)))
|-
|[[1967 Hamilton by-election]]
|37.9
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Scottish National Party))
|-
|[[2012 Bradford West by-election]]
|36.6
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Respect Party))
|-
|[[1993 Christchurch by-election]]
|35.4
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Democrats (UK)))
|-
|[[2021 North Shropshire by-election]]
|34.2
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Democrats (UK)))
|-
|[[1988 Glasgow Govan by-election]]
|33.1
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Scottish National Party))
|-
|[[1972 Sutton and Cheam by-election]]
|32.6
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Party (UK)))
|-
|[[1979 Liverpool Edge Hill by-election]]
|30.2
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Liberal Party (UK)))
|-
|[[2022 Tiverton and Honiton by-election]]
|29.9
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Democrats (UK)))
|-
|[[1994 Dudley West by-election]]
|29.2
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|[[2023 Somerton and Frome by-election]]
|29.0
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Democrats (UK)))
|-
|[[2003 Brent East by-election]]
|28.9
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Liberal Democrats (UK)))
|-
|[[1993 Newbury by-election]]
|28.4
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Democrats (UK)))
|-
|[[2014 Rochester and Strood by-election]]
|28.3((efn|group=swing|name=incmp))
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|UK Independence Party))
|-
|[[2004 Birmingham Hodge Hill by-election]]
|26.7((efn|group=swing|name=incparty|Seat was held by the incumbent party.))
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Liberal Democrats (UK)))
|-
|[[1962 Orpington by-election]]
|26.3
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Party (UK)))
|-
|[[1973 Ripon by-election]]
|25.3
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Party (UK)))
|-
|[[2021 Chesham and Amersham by-election]]
|25.1
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Democrats (UK)))
|-
|[[1991 Ribble Valley by-election]]
|24.7
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Democrats (UK)))
|-
|[[1981 Croydon North West by-election]]
|24.2
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Party (UK)))
|-
| [[2023 Tamworth by-election]]
| 23.9
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
| [[2023 Selby and Ainsty by-election]]
| 23.7
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|[[1994 Dagenham by-election]]
|23.1
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|[[1999 Hamilton South by-election]]
|22.6((efn|group=swing|name=incparty|Seat was held by the incumbent party.))
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Scottish National Party))
|-
|[[1976 Walsall North by-election]]
|22.5
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Conservative Party (UK)))
|-
|[[2008 Glasgow East by-election]]
|22.5
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Scottish National Party))
|-
|[[1996 South East Staffordshire by-election]]
|22.1
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|[[1994 Barking by-election]]
|22.0
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|[[2016 Richmond Park by-election]]
|21.7((efn|group=swing|Seat contested by the incumbent MP, who failed to gain re-election.))
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Democrats (UK)))
|-
|[[2004 Leicester South by-election]]
|21.5
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Liberal Democrats (UK)))
|-
|[[1990 Mid Staffordshire by-election]]
|21.3
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|[[1968 Dudley by-election]]
|21.2
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Conservative Party (UK)))
|-
|[[1977 Ashfield by-election]]
|20.9
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Conservative Party (UK)))
|-
|[[1999 Leeds Central by-election]]
|20.5((efn|group=swing|name=incparty|Seat was held by the incumbent party.))
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Liberal Democrats (UK)))
|-
|[[2023 Mid Bedfordshire by-election]]
|20.5
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|[[2023 Rutherglen and Hamilton West by-election]]
|20.4
| ((Party name with colour|Scottish National Party))
| ((Party name with colour|Labour Party (UK)))
|-
|[[1990 Eastbourne by-election]]
|20.0
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Democrats (UK)))
|}

((notelist|group=swing))

=== Largest swings to an incumbent governing party ===
It is rare to see any [[Swing (United Kingdom)|swing]] towards the governing party in by-elections. However, there are some examples of it happening.
{| class="wikitable sortable"
|-
!Election
!Swing
! colspan="2" |From
! colspan="2" |To
|-
|[[2021 Hartlepool by-election]]
|16.0
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Conservative Party (UK)))
|-
|[[1945 Bournemouth by-election]]
|10.3
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|[[1982 Mitcham and Morden by-election]]
|10.2
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Conservative Party (UK)))
|-
|[[1878 Worcester by-election]]
|9.9
| ((Party name with colour|Liberal Party (UK)))
| ((Party name with colour|Conservative Party (UK)))
|-
|[[2017 Copeland by-election]]
|6.7
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Conservative Party (UK)))
|-
|[[1978 Hamilton by-election]]
|4.5
| ((Party name with colour|Scottish National Party))
| ((Party name with colour|Labour Party (UK)))
|-
|[[1945 Smethwick by-election]]
|2.9
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|[[1945 Edinburgh East by-election]]
|2.0
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|[[1978 Berwick and East Lothian by-election]]
|0.8
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|}
<nowiki>*</nowiki>'''BOLD''' indicates winning party

===Largest fall in percentage share of vote===
A party's share of the vote at a general election is not always matched at subsequent by-elections, but given the five-year maximum term of a Parliament, reductions of 20% or more are unusual. Those of 25% or more are listed below:

{|class="wikitable sortable"
|-
!Election
!Fall: %
!colspan=2|Party
!colspan=2|Result
|-
|[[1948 Glasgow Camlachie by-election]]
|51.3
| ((Party name with colour|Independent Labour Party))
| ((Party name with colour|Unionist Party (Scotland))) gain
|-
|[[1983 Bermondsey by-election]]
|37.5
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Liberal Party (UK))) gain
|-
|[[1969 Birmingham Ladywood by-election]]
|33.4
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Liberal Party (UK))) gain
|-
|[[1993 Christchurch by-election]]
|32.5
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Democrats (UK))) gain
|-
|[[1946 Glasgow Bridgeton by-election]]
|32.1
| ((Party name with colour|Independent Labour Party))
| ((Party name with colour|Independent Labour Party)) hold
|-
|[[1958 Rochdale by-election]]
|31.7
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK))) gain
|-
|[[2021 North Shropshire by-election]]
|31.1
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Democrats (UK))) gain
|-
|[[1994 Dudley West by-election]]
|30.2
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK))) gain
|-
|[[1995 North Down by-election]]
|29.9
| ((Party name with colour|Northern Ireland Conservatives))
| ((Party name with colour|UK Unionist Party)) gain from [[Ulster Popular Unionist Party|Popular Unionist]]
|-
|[[1967 Hamilton by-election]]
|29.7
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Scottish National Party)) gain
|-
|[[2004 Birmingham Hodge Hill by-election]]
|29.6
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK))) hold
|-
|[[1961 Paisley by-election]]
|29.5
| ((Party name with colour|Unionist Party (Scotland)))
| ((Party name with colour|Labour Party (UK))) hold
|-
|[[2003 Brent East by-election]]
|29.4
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Liberal Democrats (UK))) gain
|-
|[[1993 Newbury by-election]]
|29.0
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Democrats (UK))) gain
|-
|[[1968 Caerphilly by-election]]
|28.7
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK))) hold
|-
|[[1999 Hamilton South by-election]]
|28.7
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK))) hold
|-
|[[2023 Mid Bedfordshire by-election]]
|28.6
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK))) gain
|-
|[[2014 Clacton by-election]]
|28.4
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|UKIP)) gain
|-
|[[1962 West Lothian by-election]]
|28.3
| ((Party name with colour|Unionist Party (Scotland)))
| ((Party name with colour|Labour Party (UK))) hold
|-
|[[1979 Liverpool Edge Hill by-election]]
|28.1
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Liberal Party (UK))) gain
|-
|[[1958 Torrington by-election]]
|27.7
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Party (UK))) gain
|-
|[[1968 Oldham West by-election]]
|27.6
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Conservative Party (UK))) gain
|-
|[[2009 Norwich North by-election]]
|26.7
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Conservative Party (UK))) gain
|-
|[[1933 Fulham East by-election]]
|26.6
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK))) gain
|-
|[[1972 Sutton and Cheam by-election]]
|26.2
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Party (UK))) gain
|-
|[[2023 Selby and Ainsty by-election]]
|26.0
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK))) gain
|-
|[[2023 Tamworth by-election]]
|25.7
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK))) gain
|-
|[[1948 Glasgow Gorbals by-election]]
|25.5
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK))) hold
|-
|[[2019 Peterborough by-election]]
|25.5
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK))) hold
|-
|[[1962 West Derbyshire by-election]]
|25.2
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Conservative Party (UK))) hold
|-
|[[2004 Leicester South by-election]]
|25.2
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Liberal Democrats (UK))) gain
|}

In the [[1934 Merthyr by-election]] the Independent Labour Party share dropped from 69.4% in the [[1931 United Kingdom general election|1931 general election]] to 9.8% (a record 59.6% loss) losing the seat to the Labour Party. However, the 1931 election had no Labour Party candidate, and the MP, [[R. C. Wallhead]], had previously been elected as a Labour candidate in prior elections, when the ILP was affiliated to Labour. Prior to his death, Wallhead joined the Labour Party, so this result could be classed as a Labour hold.

The [[1919 East Antrim by-election]] saw the [[Irish Unionist Party|Irish Unionist]] party face its first [[Unionism in Ireland|Unionist]] opposition in the seat since 1906 (in the [[1918 United Kingdom general election|1918 general election]] the heavily unionist area gave the Irish Unionist 94.6% of the vote in a contest with a Sinn Féin candidate). An [[Independent Unionist]] candidate won the seat, with the Irish Unionist share dropping by 52.8%

Worst results for other parties:

{|class="wikitable sortable"
|-
!Election
!Fall: %
!colspan=2|Party
!colspan=2|Result
|-
|[[2021 Hartlepool by-election]]((efn|group=fall|Compared with the Brexit Party candidate at the general election.))
|24.6
| ((Party name with colour|Reform UK))
| ((Party name with colour|Conservative Party (UK))) gain from Labour
|-
|[[1982 Belfast South by-election]]
|22.4
| ((Party name with colour|Ulster Unionist Party))
| ((Party name with colour|Ulster Unionist Party)) hold
|-
|[[2014 Heywood and Middleton by-election]]
|17.6
| ((Party name with colour|Liberal Democrats (UK)))
| ((Party name with colour|Labour Party (UK))) hold
|-
|[[2023 Rutherglen and Hamilton West by-election]]
|16.6
| ((Party name with colour|Scottish National Party))
| ((Party name with colour|Labour Party (UK))) gain
|-
|[[2009 Glasgow North East by-election]]
|14.0
| ((Party name with colour|Socialist Labour Party (UK)))
| ((Party name with colour|Labour Party (UK))) gain from Speaker
|-
|[[2017 Copeland by-election]]
|9.0
| ((Party name with colour|UK Independence Party))
| ((Party name with colour|Conservative Party (UK))) gain from Labour
|-
|[[1986 Newry and Armagh by-election]]
|7.7
| ((Party name with colour|Sinn Féin))
| ((Party name with colour|Social Democratic and Labour Party)) gain from Ulster Unionist
|-
|[[1963 Swansea East by-election]]
|5.3
| ((Party name with colour|Plaid Cymru))
| ((Party name with colour|Labour Party (UK))) hold
|}
((notelist|group=fall))

===Largest increase in percentage share of vote===
{|class="wikitable sortable"
|-
!Election!!Increase in Share
!colspan=2|Party
!colspan=2|Result
|-
|[[1986 East Londonderry by-election]]||56.0
| ((Party name with colour|Ulster Unionist Party))
| ((Party name with colour|Ulster Unionist Party)) hold
|-
|[[2012 Bradford West by-election]]||52.8
| ((Party name with colour|Respect Party))
| ((Party name with colour|Respect Party)) gain
|-
|[[1983 Bermondsey by-election]]||50.9
| ((Party name with colour|Liberal Party (UK)))
| ((Party name with colour|Liberal Party (UK))) gain
|-
|[[1986 South Antrim by-election]]||48.4
| ((Party name with colour|Ulster Unionist Party))
| ((Party name with colour|Ulster Unionist Party)) hold
|-
|[[1986 East Antrim by-election]]||47.5
| ((Party name with colour|Ulster Unionist Party))
| ((Party name with colour|Ulster Unionist Party)) hold
|-
|[[1986 North Antrim by-election]]||43.2
| ((Party name with colour|Democratic Unionist Party))
| ((Party name with colour|Democratic Unionist Party)) hold
|-
|[[2016 Batley and Spen by-election]]||42.6
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK))) hold
|-
|[[1972 Sutton and Cheam by-election]]||39.0
| ((Party name with colour|Liberal Party (UK)))
| ((Party name with colour|Liberal Party (UK))) gain
|-
|[[1993 Christchurch by-election]]||38.6
| ((Party name with colour|Liberal Democrats (UK)))
| ((Party name with colour|Liberal Democrats (UK))) gain
|-
|[[1988 Glasgow Govan by-election]]||38.4
| ((Party name with colour|Scottish National Party))
| ((Party name with colour|Scottish National Party)) gain
|-
|[[2022 Tiverton and Honiton by-election]]||38.1
| ((Party name with colour|Liberal Democrats (UK)))
| ((Party name with colour|Liberal Democrats (UK))) gain
|-
|[[2021 North Shropshire by-election]]||37.1
| ((Party name with colour|Liberal Democrats (UK)))
| ((Party name with colour|Liberal Democrats (UK))) gain
|-
|[[1979 Liverpool Edge Hill by-election]]||36.8
| ((Party name with colour|Liberal Party (UK)))
| ((Party name with colour|Liberal Party (UK))) gain
|-
|[[2014 Heywood and Middleton by-election]]||36.1
| ((Party name with colour|UK Independence Party))
| ((Party name with colour|Labour Party (UK))) hold
|-
|[[1986 Belfast East by-election]]||35.7
| ((Party name with colour|Democratic Unionist Party))
| ((Party name with colour|Democratic Unionist Party)) hold
|-
|[[1986 Belfast North by-election]]||35.3
| ((Party name with colour|Ulster Unionist Party))
| ((Party name with colour|Ulster Unionist Party)) hold
|-
|[[1973 Glasgow Govan by-election]]||31.6
| ((Party name with colour|Scottish National Party))
| ((Party name with colour|Scottish National Party)) gain
|-
|[[1986 Lagan Valley by-election]]||31.5
| ((Party name with colour|Ulster Unionist Party))
| ((Party name with colour|Ulster Unionist Party)) hold
|-
|[[2021 Chesham and Amersham by-election]]||30.4
| ((Party name with colour|Liberal Democrats (UK)))
| ((Party name with colour|Liberal Democrats (UK))) gain
|-
|[[1973 Ripon by-election]]||30.4
| ((Party name with colour|Liberal Party (UK)))
| ((Party name with colour|Liberal Party (UK))) gain
|-
|[[2016 Richmond Park by-election]]||30.3
| ((Party name with colour|Liberal Democrats (UK)))
| ((Party name with colour|Liberal Democrats (UK))) gain
|-
|[[1981 Croydon North West by-election]]||29.5
| ((Party name with colour|Liberal Party (UK)))
| ((Party name with colour|Liberal Party (UK))) gain
|-
|[[1968 Caerphilly by-election]]||29.3
| ((Party name with colour|Plaid Cymru))
| ((Party name with colour|Labour Party (UK))) hold
|-
|[[2003 Brent East by-election]]||28.5
| ((Party name with colour|Liberal Democrats (UK)))
| ((Party name with colour|Liberal Democrats (UK))) gain
|-
|[[1994 Dudley West by-election]]||28.0
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK))) gain
|-
|[[1987 Greenwich by-election]]||27.9
| ((Party name with colour|Social Democratic Party (UK)))
| ((Party name with colour|Social Democratic Party (UK))) gain
|-
|[[1972 Merthyr Tydfil by-election]]||27.4
| ((Party name with colour|Plaid Cymru))
| ((Party name with colour|Labour Party (UK))) gain
|-
|[[1966 Carmarthen by-election]]||27.4
| ((Party name with colour|Plaid Cymru))
| ((Party name with colour|Plaid Cymru)) gain
|-
|[[1991 Ribble Valley by-election]]||27.1
| ((Party name with colour|Liberal Democrats (UK)))
| ((Party name with colour|Liberal Democrats (UK))) gain
|-
|[[1994 Monklands East by-election]]||26.9
| ((Party name with colour|Scottish National Party))
| ((Party name with colour|Labour Party (UK))) hold
|-
|-
|[[2022 Southend West by-election]]||26.9
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Conservative Party (UK))) hold
|-
|[[2004 Birmingham Hodge Hill by-election]]||26.1
| ((Party name with colour|Liberal Democrats (UK)))
| ((Party name with colour|Labour Party (UK))) hold
|-
|[[2008 Glasgow East by-election]]||26.1
| ((Party name with colour|Scottish National Party))
| ((Party name with colour|Scottish National Party)) gain
|}

===Largest winning share of the vote===
Winning shares of the vote above 90%, since 1918:
{|class="wikitable sortable"
|-
!Candidate
!colspan=2|Party
!Election
!Votes
!% Share
|-
|[[Ernest Gates]]
| ((Party name with colour|Conservative Party (UK)))
|[[1940 Middleton and Prestwich by-election]]
|32,036
|98.7
|-
|[[Ian Paisley]]
| ((Party name with colour|Democratic Unionist Party))
|[[1986 North Antrim by-election]]
|33,937
|97.4
|-
|[[John Craik-Henderson]]
| ((Party name with colour|Conservative Party (UK)))
|[[1940 Leeds North East by-election]]
|23,882
|97.1
|-
|[[Charles Key]]
| ((Party name with colour|Labour Party (UK)))
|[[1940 Bow and Bromley by-election]]
|11,594
|95.8
|-
|[[John Taylor, Baron Kilclooney|John Taylor]]
| ((Party name with colour|Ulster Unionist Party))
|[[1986 Strangford by-election]]
|32,627
|94.2
|-
|[[Clifford Forsythe]]
| ((Party name with colour|Ulster Unionist Party))
|[[1986 South Antrim by-election]]
|30,087
|94.1
|-
|[[William Ross (Unionist politician)|William Ross]]
| ((Party name with colour|Ulster Unionist Party))
|[[1986 East Londonderry by-election]]
|30,922
|93.9
|-
|[[Arthur Woodburn]]
| ((Party name with colour|Labour Party (UK)))
|[[1939 Clackmannanshire and East Stirlingshire by-election]]
|15,645
|93.7
|-
|[[Spencer Summers]]
| ((Party name with colour|Conservative Party (UK)))
|[[1940 Northampton by-election]]
|16,587
|93.4
|-
|[[Harry Thorneycroft]]
| ((Party name with colour|Labour Party (UK)))
|[[1942 Manchester Clayton by-election]]
|8,892
|93.3
|-
|[[James Hollins]]
| ((Party name with colour|Labour Party (UK)))
|[[1940 Silvertown by-election]]
|14,343
|92.8
|-
|[[Francis Douglas, 1st Baron Douglas of Barloch|Francis Douglas]]
| ((Party name with colour|Labour Party (UK)))
|[[1940 Battersea North by-election]]
|9,947
|92.6
|-
|[[Henry Willink]]
| ((Party name with colour|Conservative Party (UK)))
|[[1940 Croydon North by-election]]
|14,163
|90.7
|-
|[[James Molyneaux, Baron Molyneaux of Killead|James Henry Molyneaux]]
| ((Party name with colour|Ulster Unionist Party))
|[[1986 Lagan Valley by-election]]
|32,514
|90.7
|-<!--
|[[Thomas Galbraith, 1st Baron Strathclyde|Thomas Galbraith]]
| ((Party name with colour|Unionist Party (Scotland)))
|[[1940 Glasgow Pollok by-election]]
|17,850
|88.1
|-
|[[William Beveridge]]
| ((Party name with colour|Liberal Party (UK)))
|[[1944 Berwick-upon-Tweed by-election]]
|8,792
|87.4
|-
|[[John Peto (politician)|John Peto]]
| ((Party name with colour|Conservative Party (UK)))
|[[1941 Birmingham King's Norton by-election]]
|21,573
|86.9
|-
|[[William Henry Guy]]
| ((Party name with colour|Labour Party (UK)))
|[[1942 Poplar South by-election]]
|3,375
|86.2
|-
|[[Tracy Brabin]]
| ((Party name with colour|Labour Party (UK)))
|[[2016 Batley and Spen by-election]]
|17,506
|85.8
|-
|[[Adam McKinlay]]
| ((Party name with colour|Labour Party (UK)))
|[[1941 Dunbartonshire by-election]]
|21,900
|85.0-->
|}

=== Largest numerical majority overturned ===
[[Plurality (voting)|Majorities]] over 9,000 votes overturned:
{| class="sortable wikitable"
|-
!Candidate
! colspan="2" |Party
!Election
!Majority overturned
!New majority
|-
|[[Alistair Strathern]]
| ((Party name with colour|Labour Party (UK)))
|[[2023 Mid Bedfordshire by-election]]
|24,664
|1,192
|-
|[[Richard Foord]]
| ((Party name with colour|Liberal Democrats (UK)))
|[[2022 Tiverton and Honiton by-election]]<ref name=":12">((cite news |last=Walker |first=Peter |date=24 June 2022 |title=Tories lose two key byelections on same night in Wakefield and Tiverton and Honiton |newspaper=[[The Guardian]] |url=https://www.theguardian.com/politics/2022/jun/24/tories-lose-byelections-wakefield-tiverton-honiton-labour-lib-dems))</ref>
|24,239
|6,144
|-
|[[Sarah Olney]]
| ((Party name with colour|Liberal Democrats (UK)))
|[[2016 Richmond Park by-election]]
|23,015
|1,872
|-
|[[Diana Maddock, Baroness Maddock|Diana Maddock]]
| ((Party name with colour|Liberal Democrats (UK)))
|[[1993 Christchurch by-election]]
|23,015
|16,427
|-
|[[Helen Morgan (politician)|Helen Morgan]]
| ((Party name with colour|Liberal Democrats (UK)))
|[[2021 North Shropshire by-election]]
|22,949
|5,925
|-
|[[Tim Smith (UK politician)|Tim Smith]]
| ((Party name with colour|Conservative Party (UK)))
|[[1977 Ashfield by-election]]
|22,915
|264
|-
|[[Keir Mather]]
| ((Party name with colour|Labour Party (UK)))
|[[2023 Selby and Ainsty by-election]]
|20,137
|4,161
|-
|[[Sarah Edwards (politician)|Sarah Edwards]]
| ((Party name with colour|Labour Party (UK)))
|[[2023 Tamworth by-election]]
|19,634
|1,316
|-
|[[Michael Carr (Liberal Democrat politician)|Michael Carr]]
| ((Party name with colour|Liberal Democrats (UK)))
|[[1991 Ribble Valley by-election]]
|19,528
|4,601
|-
|[[Jim Sillars]]
| ((Party name with colour|Scottish National Party))
|[[1988 Glasgow Govan by-election]]
|19,509
|3,554
|-
|[[Shirley Williams]]
| ((Party name with colour|Social Democratic Party (UK)))
|[[1981 Crosby by-election]]
|19,272
|5,289
|-
|[[Sarah Dyke]]
| ((Party name with colour|Liberal Democrats (UK)))
|[[2023 Somerton and Frome by-election]]
|19,213
|11,008
|-
|[[David Bellotti]]
| ((Party name with colour|Liberal Democrats (UK)))
|[[1990 Eastbourne by-election]]
|16,923
|4,550
|-
|[[Winnie Ewing]]
| ((Party name with colour|Scottish National Party))
|[[1967 Hamilton by-election]]
|16,576
|1,799
|-
|[[Sarah Green (politician)|Sarah Green]]
| ((Party name with colour|Liberal Democrats (UK)))
|[[2021 Chesham and Amersham by-election]]
|16,223
|8,028
|-
|[[Robin Hodgson]]
| ((Party name with colour|Conservative Party (UK)))
|[[1976 Walsall North by-election]]
|15,885
|4,379
|-
|[[Eric Lubbock, 4th Baron Avebury|Eric Lubbock]]
| ((Party name with colour|Liberal Party (UK)))
|[[1962 Orpington by-election]]
|14,760
|7,855
|-
|[[Sylvia Heal]]
| ((Party name with colour|Labour Party (UK)))
|[[1990 Mid Staffordshire by-election]]
|14,654
|9,449
|-
|[[John Mason (Scottish politician)|John Mason]]
| ((Party name with colour|Scottish National Party))
|[[2008 Glasgow East by-election]]
|13,507
|365
|-
|[[Sarah Teather]]
| ((Party name with colour|Liberal Democrats (UK)))
|[[2003 Brent East by-election]]
|13,047
|1,118
|-
|[[Graham Tope, Baron Tope|Graham Tope]]
| ((Party name with colour|Liberal Party (UK)))
|[[1972 Sutton and Cheam by-election]]
|12,696
|7,417
|-
|[[David Rendel]]
| ((Party name with colour|Liberal Democrats (UK)))
|[[1993 Newbury by-election]]
|12,357
|22,055
|-
|[[Parmjit Singh Gill]]
| ((Party name with colour|Liberal Democrats (UK)))
|[[2004 Leicester South by-election]]
|13,243
|1,654
|-
|[[Douglas Carswell]]
| ((Party name with colour|UK Independence Party))
|[[2014 Clacton by-election]]
|12,068
|12,404
|-
|[[David Austick]]
| ((Party name with colour|Liberal Party (UK)))
|[[1973 Ripon by-election]]
|12,064
|946
|-
|[[Simon Hughes]]
| ((Party name with colour|Liberal Party (UK)))
|[[1983 Bermondsey by-election]]
|11,756
|9,319
|-
|[[Willie Rennie]]
| ((Party name with colour|Liberal Democrats (UK)))
|[[2006 Dunfermline and West Fife by-election]]
|11,562
|1,800
|-
|[[Donald Williams (politician)|Donald Williams]]
| ((Party name with colour|Conservative Party (UK)))
|[[1968 Dudley by-election]]
|10,022
|11,656
|-
|[[Mark Reckless]]
| ((Party name with colour|UK Independence Party))
|[[2014 Rochester and Strood by-election]]
|9,953
|2,920
|}

===Lowest winning share of the vote===
Winning shares of the vote below 35%, since 1918:

{|class="sortable wikitable"
|-
!Candidate
!colspan=2|Party
!Election
!Votes
!% Share
|-
|[[Henry Strauss, 1st Baron Conesford|Henry Strauss]]
| ((Party name with colour|Conservative Party (UK)))
|[[1946 Combined English Universities by-election]]
|5,483
|30.0
|-
|[[Lisa Forbes (politician)|Lisa Forbes]]
| ((Party name with colour|Labour Party (UK)))
|[[2019 Peterborough by-election]]
|10,484 
|30.9
|-
|[[Mike Thornton (politician)|Mike Thornton]]
| ((Party name with colour|Liberal Democrats (UK)))
|[[2013 Eastleigh by-election]]
|13,342
|32.1
|-
|[[Sir Edward Campbell, 1st Baronet|Edward Campbell]]
| ((Party name with colour|Conservative Party (UK)))
|[[1930 Bromley by-election]]
|12,782
|32.4
|-
|[[George Machin]]
| ((Party name with colour|Labour Party (UK)))
|[[1973 Dundee East by-election]]
|14,411
|32.7
|-
|[[Roy Jenkins]]
| ((Party name with colour|Social Democratic Party (UK)))
|[[1982 Glasgow Hillhead by-election]]
|10,106
|33.4
|-
|[[Guy Barnett (UK politician)|Guy Barnett]]
| ((Party name with colour|Labour Party (UK)))
|[[1962 South Dorset by-election]]
|13,783
|33.5
|-
|[[Alistair Strathern]]
| ((Party name with colour|Labour Party (UK)))
|[[2023 Mid Bedfordshire by-election]]
|13,872
|34.1
|-
|[[James Carmichael (British politician)|James Carmichael]]
| ((Party name with colour|Independent Labour Party))
|[[1946 Glasgow Bridgeton by-election]]
|6,351
|34.3
|-
|[[Leah Manning]]
| ((Party name with colour|Labour Party (UK)))
|[[1931 Islington East by-election]]
|10,591
|34.7
|-
|[[Kenneth Lindsay]]
| ((Party name with colour|National Labour Organisation))
|[[1933 Kilmarnock by-election]]
|12,577
|34.8
|-
|[[Parmjit Singh Gill]]
| ((Party name with colour|Liberal Democrats (UK)))
|[[2004 Leicester South by-election]]
|10,274
|34.9
|}

The [[1920 Stockport by-election]], was held to elect two MPs. The winners' shares of the total vote were 25.6% and 25.1%. However, as each voter could cast two votes, the situation is not readily comparable to other by-elections in this period.

At the [[1909 Sheffield Attercliffe by-election]], the winning candidate took only 27.5% of the vote.

===Lowest share of the vote===

====Major parties====
Major parties winning 2% or less share of votes cast in a by-election, since 1918:

{|class="wikitable sortable"
|-
!Candidate
!colspan=2|Party
!Election
!Votes
!% Share
|-
|Geoff Juby
| ((Party name with colour|Liberal Democrats (UK)))
|[[2014 Rochester and Strood by-election]]
|349
|0.9
|-
|Lee Dargue
| ((Party name with colour|Liberal Democrats (UK)))
|[[2022 Birmingham Erdington by-election]]
|173
|1.0
|-
|Stephen Arrundale
| ((Party name with colour|Liberal Democrats (UK)))
|[[2021 Airdrie and Shotts by-election]]
|220
|1.0
|-
|Andrew Hagon
| ((Party name with colour|Liberal Democrats (UK)))
|[[2021 Hartlepool by-election]]
|349
|1.2
|-
|Roger Goodfellow
| ((Party name with colour|Liberal Party (UK)))
|[[1948 Glasgow Camlachie by-election]]
|312
|1.2
|-
|[[James Scott Duckers]]
| ((Party name with colour|Liberal Party (UK)))
|[[1924 Westminster Abbey by-election]]
|291
|1.3
|- 
|Andrew Graham
| ((Party name with colour|Liberal Democrats (UK)))
|[[2014 Clacton by-election]]
|483
|1.3
|-
|Hugh Annand
| ((Party name with colour|Liberal Democrats (UK)))
|[[2013 South Shields by-election]]
|352
|1.4
|-
|Robert McCreadie
| ((Party name with colour|Liberal Democrats (UK)))
|[[1989 Glasgow Central by-election]]
|411
|1.5
|-
|Sunny Virk
| ((Party name with colour|Liberal Democrats (UK)))
|[[2023 Tamworth by-election]]
|417
|1.6
|-
|Natasa Pantelic
| ((Party name with colour|Labour Party (UK)))
|[[2021 Chesham and Amersham by-election]]
|622
|1.6
|-
|Patrick Davies
| ((Party name with colour|Labour Party (UK)))
|[[1997 Winchester by-election]]
|944
|1.7
|-
|Blaise Baquiche
| ((Party name with colour|Liberal Democrats (UK)))
|[[2023 Uxbridge and South Ruislip by-election]]
|526
|1.7
|-
|Ian Miller
| ((Party name with colour|Liberal Party (UK)))
|[[1967 Glasgow Pollok by-election]]
|735
|1.9
|-
|Jamie Needle
| ((Party name with colour|Liberal Democrats (UK)))
|[[2022 Wakefield by-election]]
|508
|1.9
|-
|Steve Billcliffe
| ((Party name with colour|Labour Party (UK)))
|[[1993 Newbury by-election]]
|1,151
|2.0
|}

The worst Conservative performance was in the [[1995 North Down by-election]], where they took 2.1% of the votes cast.

The 'continuing' [[Social Democratic Party (UK, 1988–1990)|Social Democratic Party]] (SDP) took 0.4% of the vote at both the [[1990 Upper Bann by-election]] and the [[May 1990 Bootle by-election|Bootle by-election]] the following week.

====Candidates winning fewer than ten votes====
Since 1918:((efn|group=subten|F. R. Lees, a [[Temperance movement|Temperance]] [[Chartism|Chartist]], won no votes in the [[1860 Ripon by-election]], as his supporters mistakenly believed that he had withdrawn.))

{|class="wikitable sortable"
|-
!Votes
!Name
!Affiliation/Label
!Election
|-
|3
|Yolande Kenward
|[[Independent (politician)|''No description'']]
|[[2021 North Shropshire by-election]]
|-
|5
|[[Bill Boaks]]
|Public Safety Democratic Monarchist White Resident
|[[1982 Glasgow Hillhead by-election]]<ref name="facts">Colin Rallings and Michael Thrasher, ''British electoral facts, 1832-2006'' (Parliamentary Research Services)</ref>
|-
|5
|Smiley Smilie
|[[Independent (politician)|Independent]]
|[[2016 Tooting by-election]]
|-
|5
|[[Bobby Smith (activist)|Bobby Smith]]
|[[Independent (politician)|''No description'']]
|[[2019 Peterborough by-election]]
|-
|5
|Kailash Trivedi
|Independent Janata Party
|[[1988 Kensington by-election]]<ref name="facts" />
|-
|6
|Gary Cooke
|[[Independent (politician)|''No description'']]
|[[2023 Rutherglen and Hamilton West by-election]]
|-
|7
|John Connell
|Peace - stop ITN manipulation
|[[1984 Chesterfield by-election]]
|-
|8
|David Bishop
|[[Church of the Militant Elvis Party]]
|[[2022 Birmingham Erdington by-election]]
|-
|8
|Esmond Bevan
|Systems Designer((efn|group=subten|Bevan put his occupation of "Systems Designer" in the description field of the nomination paper, which appeared on the ballot paper. He was an independent candidate.))
|[[1983 Bermondsey by-election]]<ref name="facts" />
|-
|8
|Tony Farnon
|[[Independent (politician)|Independent]]
|[[2008 Haltemprice and Howden by-election]]
|-
|8
|77 Joseph
|[[Independent (politician)|Independent]]
|[[2023 Uxbridge and South Ruislip by-election]]
|-
|8
|[[Norman Scarth]]
|[[Independent (politician)|Independent]]
|[[2008 Haltemprice and Howden by-election]]
|-
|9
|Bobby Smith
|Bring Back Elmo
|[[2016 Tooting by-election]]
|}

((notelist|group=subten))

===Smallest majorities===
All majorities of less than 1,000 since the Second World War. Bold entries indicate a new record.

{|class="wikitable sortable"
|-
!Votes
!Election
! colspan="2" |Result
|-
|57|| '''[[1973 Berwick-upon-Tweed by-election]]'''
| ((Party name with colour|Liberal Party (UK))) gain
|-
|62||'''[[1967 Walthamstow West by-election]]'''
| ((Party name with colour|Conservative Party (UK))) gain
|-
|100||[[1986 West Derbyshire by-election]]
| ((Party name with colour|Conservative Party (UK))) hold
|-
|205||'''[[1965 Leyton by-election]]'''
| ((Party name with colour|Conservative Party (UK))) gain
|-
|219||'''[[1958 Torrington by-election]]'''
| ((Party name with colour|Liberal Party (UK))) gain
|-
|220||[[1962 Central Norfolk by-election]]
| ((Party name with colour|Conservative Party (UK))) hold
|-
|264||[[1977 Ashfield by-election]]
| ((Party name with colour|Conservative Party (UK))) gain
|-
|289||[[1982 Birmingham Northfield by-election]]
| ((Party name with colour|Labour Party (UK))) gain
|-
|293||'''[[1950 Dunbartonshire West by-election]]'''
| ((Party name with colour|Labour Party (UK))) hold
|-
|323||[[2021 Batley and Spen by-election]]
| ((Party name with colour|Labour Party (UK))) hold
|-
|359||'''[[1946 Combined English Universities by-election]]'''
| ((Party name with colour|Conservative Party (UK))) gain
|-
|365||[[2008 Glasgow East by-election]]
| ((Party name with colour|Scottish National Party)) gain
|-
|395||[[1948 Glasgow Camlachie by-election]]
| ((Party name with colour|Unionist Party (Scotland))) gain
|-
|430||[[1980 Southend East by-election]]
| ((Party name with colour|Conservative Party (UK))) hold
|-
|437||[[1950 Brighouse and Spenborough by-election]]
| ((Party name with colour|Labour Party (UK))) hold
|-
|452||data-sort-value=0 | '''[[1946 Heywood and Radcliffe by-election]]'''
| ((Party name with colour|Labour Party (UK))) hold
|-
|460||[[2004 Birmingham Hodge Hill by-election]]
| ((Party name with colour|Labour Party (UK))) hold
|-
|478||[[1969 Swindon by-election]]
| ((Party name with colour|Conservative Party (UK))) gain
|-
|495
|[[2023 Uxbridge and South Ruislip by-election]]
| ((Party name with colour|Conservative Party (UK))) hold
|-
|517||[[1969 Paddington North by-election]]
| ((Party name with colour|Labour Party (UK))) hold
|-
|520||[[1977 Grimsby by-election]]
| ((Party name with colour|Labour Party (UK))) hold
|-
|552||[[1983 Penrith and The Border by-election]]
| ((Party name with colour|Conservative Party (UK))) hold
|-
|556||[[1999 Hamilton South by-election]]
| ((Party name with colour|Labour Party (UK))) hold
|-
|557||[[1967 Manchester Gorton by-election]]
| ((Party name with colour|Labour Party (UK))) hold
|-
|559||[[1985 Brecon and Radnor by-election]]
| ((Party name with colour|Liberal Party (UK))) gain
|-
|571||[[1973 Glasgow Govan by-election]]
| ((Party name with colour|Scottish National Party)) gain
|-
|617||[[2014 Heywood and Middleton by-election]]
| ((Party name with colour|Labour Party (UK))) hold
|-
|633||[[2006 Bromley and Chislehurst by-election]]
| ((Party name with colour|Conservative Party (UK))) hold
|-
|641||[[1960 Bolton East by-election]]
| ((Party name with colour|Conservative Party (UK))) hold
|-
|657||[[1956 Taunton by-election]]
| ((Party name with colour|Conservative Party (UK))) hold
|-
|666||[[1960 Brighouse and Spenborough by-election]]
| ((Party name with colour|Conservative Party (UK))) gain
|-
|683||[[2019 Peterborough by-election]]
| ((Party name with colour|Labour Party (UK))) hold
|-
|704||[[1962 South Dorset by-election]]
| ((Party name with colour|Labour Party (UK))) gain
|-
|705||[[2000 Falkirk West by-election]]
| ((Party name with colour|Labour Party (UK))) hold
|-
|740||[[1968 Bassetlaw by-election]]
| ((Party name with colour|Labour Party (UK))) hold
|-
|799||[[1986 Newcastle-under-Lyme by-election]]
| ((Party name with colour|Labour Party (UK))) hold
|-
|806||[[1955 Mid Ulster by-election]]
| ((Party name with colour|Sinn Féin)) hold
|-
|815||[[1988 Kensington by-election]]
| ((Party name with colour|Conservative Party (UK))) hold
|-
|822||[[2000 South Antrim by-election]]
| ((Party name with colour|Democratic Unionist Party)) gain
|-
|865||[[1955 South Norfolk by-election]]
| ((Party name with colour|Conservative Party (UK))) hold
|-
|913||[[1950 Belfast West by-election]]
| ((Party name with colour|Ulster Unionist Party)) hold
|-
|917||[[1962 South Northamptonshire by-election]]
| ((Party name with colour|Conservative Party (UK))) hold
|-
|946||[[1973 Ripon by-election]]
| ((Party name with colour|Liberal Party (UK))) gain
|-
|971||[[1963 Dumfriesshire by-election]]
| ((Party name with colour|Unionist Party (Scotland))) hold
|-
|973||[[1962 Blackpool North by-election]]
| ((Party name with colour|Conservative Party (UK))) hold
|}
Still smaller majorities have been recorded since 1918. The majority in the [[1921 Penrith and Cockermouth by-election]], was only 31 votes, and in the [[1924 Westminster Abbey by-election]] it was 43 votes, while at the [[1928 Carmarthen by-election]] it was 47 votes.<ref name="facts" /> At the [[1892 Cirencester by-election]] a majority of 3 for the Unionists was overturned on petition, where it was found that both candidates had an equal number of votes. A fresh by-election was called, which was won by the Liberals. The [[1830 Liverpool by-election]] saw a majority of 29 votes.<ref name="stooks-smith">((cite book |last=Stooks Smith |first=Henry. |url=https://archive.org/details/parliamentsofeng0000smit/page/180 |title=The Parliaments of England |publisher=Parliamentary Research Services |year=1973 |isbn=0-900178-13-2 |editor-last=Craig |editor-first=F. W. S. |editor-link=F. W. S. Craig |edition=2nd |location=Chichester |pages=[https://archive.org/details/parliamentsofeng0000smit/page/180 180–184] |orig-year=1844–1850))</ref>

===Turnout===
Turnout is the percentage of registered electors who voted.

====Highest turnout====
The highest turnouts since 1918.

{|class="wikitable sortable"
!By-election
!Year
!Turnout %
|-
|[[1969 Mid Ulster by-election]]
|1969
|91.5%
|-
|[[1955 Mid Ulster by-election]]
|1955
|89.7%
|-
|[[1928 Ashton-under-Lyne by-election]]
|1928
|89.1%<ref name="facts" />
|-
|[[August 1981 Fermanagh and South Tyrone by-election|1981 (August) Fermanagh and South Tyrone by-election]]
|1981
|88.6%
|-
|[[1956 Mid Ulster by-election]]
|1956
|88.4%
|-
|[[1923 Tiverton by-election]]
|1923
|88.1%<ref name="facts" />
|-
|[[1926 Darlington by-election]]
|1926
|87.6%<ref name="facts" />
|-
|[[1957 Carmarthen by-election]]
|1957
|87.4%<ref name="facts" />
|-
|[[April 1981 Fermanagh and South Tyrone by-election|1981 (April) Fermanagh and South Tyrone by-election]]
|1981
|86.9%
|-
|[[1925 Stockport by-election]]
|1925
|85.7%<ref name="facts" />
|-
|[[1950 Brighouse and Spenborough by-election]]
|1950
|85.4%<ref name="facts" />
|}

====Turnout increased from general election====
It is highly unusual for a by-election to attract a higher turnout in a seat than the previous general election.

{|class="wikitable sortable"
!By-election
!Turnout %
!Turnout %<br />at general election
!Increase %
|-
|[[1936 Ross and Cromarty by-election]]
|65.2
|50.8
|14.4
|-
|[[1958 Torrington by-election]]
|80.6
|69.2
|11.4
|-
|[[1938 Bridgwater by-election]]
|82.3
|72.7
|9.6
|-
|[[1938 Oxford by-election]]
|76.3
|67.3
|9.0
|-
|[[1928 Carmarthen by-election]]
|76.6
|67.9
|8.7
|-
|[[1928 St Ives by-election]]
|77.4
|69.1
|8.3
|-
|[[1969 Mid Ulster by-election]]
|91.5
|83.9
|7.6
|-
|[[1958 East Aberdeenshire by-election]]
|65.9
|59.8
|6.1
|-
|[[1926 Kingston upon Hull Central by-election]]
|82.8
|77.1
|5.7
|-
|[[1927 Bosworth by-election]]
|84.6
|80.8
|3.8
|-
|[[1927 Leith by-election]]
|73.9
|70.5
|3.4
|-
|[[1932 Cardiganshire by-election]]
|70.4
|67.5
|2.9
|-
|[[1929 North Lanarkshire by-election]]
|82.3
|79.9
|2.4
|-
|[[1957 Carmarthen by-election]]
|87.4
|85.1
|2.3
|-
|[[1948 Paisley by-election]]
|76.0
|73.9
|2.1
|-
|[[1967 Rhondda West by-election]]
|82.2
|80.3
|1.9
|-
|[[1948 Croydon North by-election]]
|74.8
|73.2
|1.6
|-
|[[August 1981 Fermanagh and South Tyrone by-election|1981 (August) Fermanagh and South Tyrone by-election]]
|88.6
|87.1
|1.5
|-
|[[1926 Darlington by-election]]
|87.6
|86.1
|1.5
|-
|[[1928 Linlithgowshire by-election]]
|81.5
|80.0
|1.5
|-
|[[1973 Berwick-upon-Tweed by-election]]
|75.0
|73.7
|1.3
|-
|[[1970 South Ayrshire by-election]]
|76.3
|75.1
|1.2
|-
|[[1955 Mid Ulster by-election]]
|89.7
|88.6
|1.1
|-
|[[1948 Wigan by-election]]
|81.4
|80.4
|1.0
|-
|[[1986 Newry and Armagh by-election]]
|76.9
|76.0
|0.9
|-
|[[1928 Ashton-under-Lyne by-election]]
|89.1
|88.3
|0.8
|-
|[[1977 Great Grimsby by-election]]
|70.2
|69.4
|0.8
|-
|[[1938 Ipswich by-election]]
|82.8
|82.1
|0.7
|-
|[[1982 Glasgow Hillhead by-election]]
|76.4
|75.7
|0.7
|-
|[[1938 Walsall by-election]]
|75.9
|75.2
|0.7
|-
|[[1958 Argyll by-election]]
|67.1
|66.6
|0.5
|-
|[[1926 Smethwick by-election]]
|78.6
|78.2
|0.4
|-
|[[1967 Hamilton by-election]]
|73.7
|73.3
|0.4
|-
|[[1971 Macclesfield by-election]]
|76.6
|76.4
|0.2
|}

====Lowest turnout====
During the Second World War the electoral register was not kept up to date despite significant population movements, especially in the London area (which contains all three constituencies in the first list below). Consequently, only those eligible to vote in the constituency at the outbreak of war were eligible to vote in the by-elections, and many of those were physically unable to vote, as they were located elsewhere; in addition the major parties did not compete against each other. The lowest turnout in peacetime since 1918 was 18.2% at the [[2012 Manchester Central by-election]].<ref>((cite web|title=Labour holds in Cardiff and Manchester but turnout is low|date=16 November 2012|url=http://www.channel4.com/news/labour-holds-cardiff-and-manchester-seats|publisher=Channel 4 News|access-date=16 November 2012))</ref> The lowest turnouts since 1918 have been:

*[[1942 Poplar South by-election]]: 8.5%<ref name="facts" />
*[[1941 Harrow by-election]]: 10.7% 
*[[1944 Camberwell North by-election]]: 11.2%

Turnouts of less than 30% since 1945 (bold indicates a new post-war record)
{|class="wikitable sortable"
!By-election
!Turnout %
|-
|'''[[2012 Manchester Central by-election]]'''
|18.2%
|-
|'''[[1999 Leeds Central by-election]]'''
|19.6%
|-
|[[2022 Southend West by-election]]
|24.0%
|-
|'''[[1958 Shoreditch and Finsbury by-election]]'''
|24.9%
|-
|[[1999 Wigan by-election]]
|25.0%
|-
|[[2000 Tottenham by-election]]
|25.4%
|-
|[[2012 Cardiff South and Penarth by-election]]
|25.7%
|-
|[[2016 Batley and Spen by-election]]
|25.8%
|-
|[[2022 Stretford and Urmston by-election]]
|25.8%
|-
|[[1974 Newham South by-election]]
|25.9%
|-
|[[2012 Middlesbrough by-election]]
|26.0%
|-
|[[2012 Croydon North by-election]]
|26.5%
|-
|[[2022 Birmingham Erdington by-election]]
|27.0%
|-
|[[2000 West Bromwich West by-election]]
|27.6%
|-
|[[2011 Feltham and Heston by-election]]
|28.8%
|-
|[[2000 Preston by-election]]
|29.6%
|-
|[[1999 Kensington and Chelsea by-election]]
|29.7%
|}

===Most candidates===

Under current UK electoral law there is no upper or lower limit for candidature numbers, with the only required stipulation being the valid nomination of ten electors from the constituency. By-elections often attract "fringe" or novelty candidates, single-issue candidates, or independents. As with nominations in a general election, candidates must pay a £500 [[Deposit (politics)|deposit]], which is only refunded if the candidate wins 5% of the votes cast.

All by-elections with more than ten candidates are listed. Elections are listed in alphabetical order. Those that created a new record number appear in bold.

In 2017, the countermanded poll in [[2017 Manchester Gorton by-election|Manchester Gorton]] had 11 candidates.

{| class="wikitable"
|-
!width="50"|Year
! style="width:100px;"|Number of candidates
! style="width:225px;"|Election
|-
|2008|| 26 || '''[[2008 Haltemprice and Howden by-election|Haltemprice and Howden]]'''
|-
|1993|| 19 || '''[[1993 Newbury by-election|Newbury]]'''
|-
|1999|| 18 || [[1999 Kensington and Chelsea by-election|Kensington and Chelsea]]
|-
|2023|| rowspan="2" |  17 ||[[2023 Uxbridge and South Ruislip by-election|Uxbridge and South Ruislip]]
|-
|1984 ||  '''[[1984 Chesterfield by-election|Chesterfield]]'''
|-
|2021|| rowspan="4" | 16 || [[2021 Batley and Spen by-election|Batley and Spen]] 
|-
|1983||'''[[1983 Bermondsey by-election|Bermondsey]]'''
|-
|2003|| [[2003 Brent East by-election|Brent East]]
|-
|2021|| [[2021 Hartlepool by-election|Hartlepool]] 
|-
|1988|| rowspan="3" | 15 || [[1988 Kensington by-election|Kensington]]
|-
|2019|| [[2019 Peterborough by-election|Peterborough]]
|-
|2022|| [[2022 Wakefield by-election|Wakefield]]
|-
|1993|| rowspan="11" | 14 || [[1993 Christchurch by-election|Christchurch]]
|-
|2012|| [[2012 Corby by-election|Corby]]
|-
|2013|| [[2013 Eastleigh by-election|Eastleigh]]
|-
|2004|| [[2004 Hartlepool by-election|Hartlepool]]
|-
|2018|| [[2018 Lewisham East by-election|Lewisham East]]
|-
|1990|| [[1990 Mid Staffordshire by-election|Mid Staffordshire]]
|-
|2021|| [[2021 North Shropshire by-election|North Shropshire]]
|-
|2023|| [[2023 Rutherglen and Hamilton West by-election|Rutherglen and Hamilton West]]
|-
|2016|| [[2016 Tooting by-election|Tooting]]
|-
|1989|| [[1989 Vauxhall by-election|Vauxhall]]
|-
|2016|| [[2016 Witney by-election|Witney]]
|-
|2009|| rowspan= "5" | 13 || [[2009 Glasgow North East by-election|Glasgow North East]]
|-
|2023|| [[2023 Mid Bedfordshire by-election|Mid Bedfordshire]]
|-
|2014|| [[2014 Rochester and Strood by-election|Rochester and Strood]]
|- 
|2023|| [[2023 Selby and Ainsty by-election|Selby and Ainsty]]
|-
|1996|| [[1996 South East Staffordshire by-election|South East Staffordshire]]
|-
|2022|| rowspan="9" | 12 || [[2022 Birmingham Erdington by-election|Birmingham Erdington]] 
|-
|2012|| [[2012 Croydon North by-election|Croydon North]]
|-
|1981|| '''[[1981 Croydon North West by-election|Croydon North West]]'''
|-
|2003|| [[2007 Ealing Southall by-election|Ealing Southall]]
|-
|1999|| [[1999 Hamilton South by-election|Hamilton South]]
|-
|2008 || [[2008 Henley by-election|Henley]]
|-
|2012 || [[2012 Manchester Central by-election|Manchester Central]]
|-
|2009 || [[2009 Norwich North by-election|Norwich North]]
|-
|1997|| [[1997 Wirral South by-election|Wirral South]]
|-
|2006|| rowspan="15" | 11 || [[2006 Bromley and Chislehurst by-election|Bromley and Chislehurst]]
|-
|1986|| [[1986 Fulham by-election|Fulham]]
|-
|1978 || '''[[1978 Lambeth Central by-election|Lambeth Central]]'''
|-
|2004 || [[2004 Leicester South by-election|Leicester South]]
|-
|2014|| [[2014 Newark by-election|Newark]]
|-
|2019|| [[2019 Newport West by-election|Newport West]]
|-
|2021||[[2021 Old Bexley and Sidcup by-election|Old Bexley and Sidcup]] 
|-
|2024||[[2024 Rochdale by-election|Rochdale]]
|-
|2012 || [[2012 Rotherham by-election|Rotherham]]
|-
|2007 || [[2007 Sedgefield by-election|Sedgefield]]
|-
|1990 || [[1990 Upper Bann by-election|Upper Bann]]
|-
|1997 || [[1997 Uxbridge by-election|Uxbridge]]
|-
|1989 || [[1989 Vale of Glamorgan by-election|Vale of Glamorgan]]
|-
|1981 || [[1981 Warrington by-election|Warrington]]
|-
|2024 || [[2024 Wellingborough by-election|Wellingborough]]
|-
|2016 || rowspan="13" | 10 || [[2016 Batley and Spen by-election|Batley and Spen]]
|-
|1977 || [[1977 Birmingham Ladywood by-election|Birmingham Ladywood]]
|-
|1990 || [[1990 Bradford North by-election|Bradford North]]
|-
|1977 || '''[[1977 City of London and Westminster South by-election|City of London and Westminster South]]'''
|-
|2008 || [[2008 Crewe and Nantwich by-election|Crewe and Nantwich]]
|-
|1994 || [[1994 Dudley West by-election|Dudley West]]
|-
|1996 || [[1996 Hemsworth by-election|Hemsworth]]
|-
|1995 || [[1995 Littleborough and Saddleworth by-election|Littleborough and Saddleworth]]
|-
|2005 || [[2005 Livingston by-election|Livingston]]
|-
|2002 || [[2002 Ogmore by-election|Ogmore]]
|-
|2010 || [[2011 Oldham East and Saddleworth by-election|Oldham East and Saddleworth]]
|-
|2016 || [[2016 Sleaford and North Hykeham by-election|Sleaford and North Hykeham]]
|-
|2017 || [[2017 Stoke-on-Trent Central by-election|Stoke-on-Trent Central]]
|}

===Fewest candidates===

{| class="wikitable"
|-
!width="50"|Year
! style="width:100px;"|Number of candidates
! style="width:225px;"|Election
|-
|1954|| rowspan="5" |1 ([[Uncontested election|uncontested]])||[[1954 Armagh by-election|Armagh]]<ref name="stats38">((cite book|last1=Craig|first1=F. W. S.|title=British Parliamentary Election Statistics 1918-1968|url=https://archive.org/details/britishparliamen0000crai_h0w9|url-access=registration|date=1968|publisher=Political Reference Publications|location=Glasgow|isbn=0900178000|page=[https://archive.org/details/britishparliamen0000crai_h0w9/page/38 38]))</ref>
|-
|1953||[[1953 North Down by-election|North Down]]<ref name="stats38" />
|-
|1952||[[1952 North Antrim by-election|North Antrim]]<ref name="stats38" />
|-
|1951||[[1951 Londonderry by-election|Londonderry]]<ref name="stats38" />
|-
|1946||[[1946 Hemsworth by-election|Hemsworth]]<sup>1</sup><ref name="stats38" />
|-
|1986|| rowspan="3" | 2 || [[1986 Northern Ireland by-elections|Eight of the Northern Ireland by-elections]]<sup>2</sup>
|-
|1981 ||[[April 1981 Fermanagh and South Tyrone by-election|Fermanagh and South Tyrone]]
|-
|1971 ||[[1971 Widnes by-election|Widnes]]<sup>1</sup>
|-
|1986 || 3 || [[1986 Ryedale by-election|Ryedale]]
|}

:<nowiki>*</nowiki><sup>1</sup> The most recent mainland UK instance only is given.
:<nowiki>*</nowiki><sup>2</sup> Four of these eight were between the Unionist incumbent and a "[[paper candidate]]" using the name "[[Peter Barry (politician)|Peter Barry]]", the name of the then Irish Minister of Foreign Affairs.

==Candidate records==

===Durable by-election candidates===

====Major parties====
Former Labour cabinet minister [[Tony Benn]] contested no fewer than four by-elections during his career, topping the poll on each occasion: [[Bristol South East (UK Parliament constituency)|Bristol South East]] in [[1950 Bristol South East by-election|1950]], [[1961 Bristol South East by-election|1961]] and [[1963 Bristol South East by-election|1963]], and [[1984 Chesterfield by-election|Chesterfield in 1984]]. His first and last by-election victories were 33 years and 3 months apart.

Former cabinet minister and European Commissioner [[Roy Jenkins]] fought two different by-elections for the [[Social Democratic Party (UK)|Social Democratic Party]] only eight months apart. He narrowly failed in the [[1981 Warrington by-election]] before winning the [[1982 Glasgow Hillhead by-election]]. He had been first elected as a Labour MP almost 34 years previously in the [[1948 Southwark Central by-election]].

Former [[Speaker of the House of Commons (United Kingdom)|Speaker of the House of Commons]], [[Betty Boothroyd]] finally secured election at her third by-election attempt at the [[1973 West Bromwich by-election]]. She had previously failed in the [[1957 Leicester South East by-election]] and the [[1968 Nelson and Colne by-election]] as well as the general elections of 1959 and 1970.

John Bickley of [[United Kingdom Independence Party|UKIP]] contested three by-elections (all in [[Greater Manchester]]) within two years - [[2014 Wythenshawe and Sale East by-election|Wythenshawe and Sale East]] in February 2014, [[2014 Heywood and Middleton by-election|Heywood and Middleton]] in October 2014 and [[2015 Oldham West and Royton by-election|Oldham West and Royton]] in December 2015. He was defeated on each occasion, coming closest in Heywood and Middleton where he lost by less than 700 votes. Bickley also contested Heywood and Middleton at the [[2015 United Kingdom general election|2015 general election]], making a total of four parliamentary elections contested in fewer than 24 months.

====Minor parties and independents====
Perennial fringe candidates include such personalities as [[Bill Boaks]], whose highest vote was at the [[1982 Beaconsfield by-election]] with 99 votes. [[Screaming Lord Sutch]] was for most of his career the leader of the [[Official Monster Raving Loony Party]]. His highest vote total was 1,114 at the [[1994 Rotherham by-election]]. [[Lindi St Clair]] of the Corrective Party contested eleven by-elections without success, her highest total being 216 votes as 'Lady Whiplash' at the [[1990 Eastbourne by-election]]. Sutch's successor as leader of the Official Monster Raving Loony Party, [[Howling Laud Hope|Alan "Howling Laud" Hope]], has, as of the [[2023 Uxbridge and South Ruislip by-election]], contested twenty-one by-elections.<ref>[http://ukpollingreport.co.uk/2015guide/south-shields-by-election/ South Shields by-election] UK Polling Report</ref>

Under various ballot paper descriptions, David Bishop of the [[Church of the Militant Elvis]] label stood at seven by-elections, receiving 99 votes at the [[2012 Corby by-election]], an increase over his previous high of 93 at the [[2011 Feltham and Heston by-election]].

====Pre-1945====
[[Arthur Henderson]] was distinguished in being successful in no fewer than five by-elections in different seats, in [[Barnard Castle (UK Parliament constituency)|Barnard Castle]], [[Widnes (UK Parliament constituency)|Widnes]], [[Newcastle-upon-Tyne East (UK Parliament constituency)|Newcastle upon Tyne East]], [[Burnley (UK Parliament constituency)|Burnley]], and [[Clay Cross (UK Parliament constituency)|Clay Cross]].

[[Joseph Gibbins]] is the only person in modern times to gain the same seat twice in two different by-elections. He triumphed for Labour in the [[1924 Liverpool West Toxteth by-election|1924]] and [[1935 Liverpool West Toxteth by-election|1935 Liverpool West Toxteth by-elections]].

[[William O'Brien]] won four by-elections, in [[1883 Mallow by-election|Mallow in 1883]], [[1887 North East Cork by-election|North East Cork in 1887]] and then [[Cork City (UK Parliament constituency)|Cork City]] in [[1904 Cork City by-election|1904]] and [[1914 Cork City by-election|1914]]. On these last two occasions, he was re-elected having resigned the seat.

Prime Minister [[Winston Churchill]] contested five by-elections in his long career:
*[[1899 Oldham by-election]] in which he was not elected
*[[1908 Manchester North West by-election]] where he was defeated
*[[1908 Dundee by-election]] where he was elected
*[[1917 Dundee by-election]] where he was re-elected.<ref>[[Roy Jenkins]] ''Churchill'' ([[Macmillan Publishers|Macmillan]], 2001), page 325 ((ISBN|0-333-78290-9))</ref>
*[[1924 Westminster Abbey by-election]] in which he was unsuccessful

[[John Wilkes]] won the [[1757 Aylesbury by-election]], and was then elected in the [[1769 Middlesex by-elections|Middlesex by-elections]] of February, March and April 1769, on each occasion being subsequently expelled from the House of Commons.

===Former MPs making a comeback at a by-election===
{|class="wikitable sortable"
|-
!Election
!MP
!colspan=2|Party
!notes
|-
|[[2012 Bradford West by-election]]<sup>1</sup>
|[[George Galloway]]
| ((Party name with colour|Respect Party))
|returns after failing to win a seat in the 2010 general election
|-
|[[2000 South Antrim by-election]]<sup>1</sup>
|[[William McCrea, Baron McCrea of Magherafelt and Cookstown|William McCrea]]
| ((Party name with colour|Democratic Unionist Party)) 
|returns after losing his [[Mid Ulster (UK Parliament constituency)|Mid Ulster]] seat in the 1997 general election. 
|-
|[[1999 Kensington and Chelsea by-election]]
|[[Michael Portillo]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing his [[Enfield Southgate]] seat at the 1997 general election.
|-
|[[1997 Beckenham by-election]]
|[[Jacqui Lait]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing her [[Hastings and Rye]] seat at the 1997 general election.
|-
|[[1988 Epping Forest by-election]]
|[[Steve Norris]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing his [[Oxford East]] seat at the 1987 general election.
|-
|[[1988 Glasgow Govan by-election]]<sup>1</sup>
|[[Jim Sillars]]
| ((Party name with colour|Scottish National Party))
|He had first sat as a Labour MP (later as [[Scottish Labour Party (1976)|Scottish Labour]]) for [[South Ayrshire]] between 1970 and 1979.
|-
|[[1984 Chesterfield by-election]]
|[[Tony Benn]]
| ((Party name with colour|Labour Party (UK)))
|returns after losing his redrawn [[Bristol East]] seat at the 1983 general election.
|-
|[[1982 Beaconsfield by-election]]
|[[Tim Smith (UK politician)|Tim Smith]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing his [[Ashfield (UK Parliament constituency)|Ashfield]] seat in the 1979 general election.
|-
|[[1982 Glasgow Hillhead by-election]]<sup>2</sup>: 
|[[Roy Jenkins]]
| ((Party name with colour|Social Democratic Party (UK)))
|returns after a spell as [[European Commissioner]], then co-founding the Social Democratic Party (SDP). He had first sat as a Labour MP for [[Southwark Central]] from 1948 to 1950 and [[Birmingham Stechford (UK Parliament constituency)|Birmingham Stechford]] from 1950 to 1977.
|-
|[[1981 Crosby by-election]]<sup>1</sup>
|[[Shirley Williams]]
| ((Party name with colour|Social Democratic Party (UK)))
|returns as the first-elected SDP MP. She had first sat as a Labour MP for [[Hitchin (UK Parliament constituency)|Hitchin]] 1964-74 and for [[Hertford and Stevenage]] 1974-79
|-
|[[1981 Warrington by-election]]
|[[Douglas Hoyle]]
| ((Party name with colour|Labour Party (UK)))
|returns after losing his [[Nelson and Colne]] seat in the 1979 general election.
|-
|[[1980 Southend East by-election]]
|[[Teddy Taylor]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing his [[Glasgow Cathcart (UK Parliament constituency)|Glasgow Cathcart]] seat at the 1979 general election
|-
|[[1979 South West Hertfordshire by-election]]
|[[Richard Page]]
| ((Party name with colour|Conservative Party (UK)))
| returns after losing his [[Workington]] seat in the 1979 general election
|-
|[[1979 Knutsford by-election]]
|[[Jock Bruce-Gardyne]]
| ((Party name with colour|Conservative Party (UK)))
| returns after losing his [[South Angus]] seat at the October 1974 general election.
|-
|[[1979 Clitheroe by-election]]
|[[David Waddington, Baron Waddington|David Waddington]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing his [[Nelson and Colne]] seat at the October 1974 general election.
|-
|[[1978 Glasgow Garscadden by-election]]
|[[Donald Dewar]]
| ((Party name with colour|Labour Party (UK)))
|returns after losing his [[Aberdeen South (UK Parliament constituency)|Aberdeen South]] seat in the 1970 general election.
|-
|[[1977 Saffron Walden by-election]]
|[[Alan Haselhurst]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing his [[Middleton and Prestwich (UK Parliament constituency)|Middleton and Prestwich]] seat in the February 1974 general election.
|-
|[[1974 Newham South by-election]]
|[[Nigel Spearing]]
| ((Party name with colour|Labour Party (UK)))
|returns after losing his [[Acton, London|Acton]] seat in the February 1974 general election.
|-
|[[1972 Merthyr Tydfil by-election]]<sup>2</sup>
|[[Edward Rowlands]]
| ((Party name with colour|Labour Party (UK)))
|returns after losing his [[Cardiff North (UK Parliament constituency)|Cardiff North]] seat in the 1970 general election.
|-
|[[1971 Greenwich by-election]]
|[[Guy Barnett (UK politician)|Guy Barnett]]
| ((Party name with colour|Labour Party (UK)))
|returns after losing his [[South Dorset]] seat in the 1964 general election.
|-
|[[1971 Southampton Itchen by-election]]
|[[Bob Mitchell (UK politician)|Bob Mitchell]]
| ((Party name with colour|Labour Party (UK)))
|returns after losing his [[Southampton Test]] seat in the 1970 general election.
|-
|[[1970 St Marylebone by-election]]
|[[Kenneth Baker, Baron Baker of Dorking|Kenneth Baker]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing his [[Acton, London|Acton]] seat in the 1970 general election.
|-
|[[1969 Chichester by-election]]
|[[Christopher Chataway]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing his [[Lewisham North (UK Parliament constituency)|Lewisham North]] seat in the 1966 general election.
|-
|[[1969 Brighton Pavilion by-election]]
|[[Julian Amery]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing his [[Preston North]] seat in the 1966 general election.
|-
|[[1968 New Forest by-election]]
|[[Patrick McNair-Wilson]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing his [[Lewisham West (UK Parliament constituency)|Lewisham West]] seat in the 1966 general election.
|-
|[[1968 Warwick and Leamington by-election]]
|[[Dudley Smith]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing his [[Brentford and Chiswick (UK Parliament constituency)|Brentford and Chiswick]] seat in the 1966 general election.
|-
|[[1967 West Derbyshire by-election]]
|[[James Scott-Hopkins]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing his [[Cornwall North (UK Parliament constituency)|Cornwall North]] seat in the 1966 general election.
|-
|[[1967 Brierley Hill by-election]]
|[[Fergus Montgomery]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing his [[Newcastle upon Tyne East]] seat in the 1964 general election.
|-
|[[1967 Honiton by-election]]
|[[Peter Emery]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing his [[Reading, Berkshire|Reading]] seat in the 1966 general election.
|-
|[[1965 Saffron Walden by-election]]
|[[Peter Michael Kirk|Peter Kirk]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing his [[Gravesend, Kent|Gravesend]] seat in the 1964 general election.
|-
|[[1965 Salisbury by-election]]
|[[Michael Hamilton (politician)|Michael Hamilton]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing his [[Wellingborough]] seat in the 1964 general election.
|-
|[[1965 East Grinstead by-election]]
|[[Geoffrey Johnson-Smith]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing his [[Holborn and St. Pancras South]] seat in the 1964 general election.
|-
|[[1965 Altrincham and Sale by-election]]
|[[Anthony Barber]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing his [[Doncaster]] seat in the 1964 general election.
|-
|[[1963 St Marylebone by-election]]
|[[Quintin Hogg, Baron Hailsham of St Marylebone|Quintin Hogg]]
| ((Party name with colour|Conservative Party (UK)))
|returns after disclaiming his peerage. He had previously sat for [[Oxford (UK Parliament constituency)|Oxford]] 1938–1950.
|-
|[[1963 Kinross and Western Perthshire by-election]]
|Sir [[Alec Douglas-Home]]
| ((Party name with colour|Unionist Party (Scotland)))
|returns after disclaiming his peerage. He had previously sat for [[Lanark (UK Parliament constituency)|Lanark]] 1931-45 and 1950–51.
|-
|[[1963 Bristol South East by-election]]
|[[Tony Benn]]
| ((Party name with colour|Labour Party (UK)))
|returns after disclaiming his peerage. He had been disqualified after the death of his father in 1960, and his election in a [[1961 Bristol South East by-election|1961 by-election]] had been adjudged undue on petition.
|-
|[[1962 Middlesbrough East by-election]]
|[[Arthur Bottomley]]
| ((Party name with colour|Labour Party (UK)))
|returns after losing his [[Rochester and Chatham (UK Parliament constituency)|Rochester and Chatham]] seat in the 1959 general election.
|-
|[[1960 Ebbw Vale by-election]]
|[[Michael Foot]]
| ((Party name with colour|Labour Party (UK)))
|returns after losing his [[Plymouth Devonport (UK Parliament constituency)|Plymouth Devonport]] seat in the 1955 general election.
|-
|[[1956 Newport by-election]]
|[[Frank Soskice]] 
| ((Party name with colour|Labour Party (UK)))
|returns after his [[Sheffield Neepsend (UK Parliament constituency)|Sheffield Neepsend]] seat was abolished at the 1955 general election.
|-
|[[1950 Sheffield Neepsend by-election]]
|[[Frank Soskice]]
| ((Party name with colour|Labour Party (UK)))
|returns after his [[Birkenhead East (UK Parliament constituency)|Birkenhead East]] seat was abolished at the 1950 general election.
|-
|[[1913 Houghton-le-Spring by-election]]<sup>1</sup>
|[[Thomas Edward Wing]]
| ((Party name with colour|Liberal Party (UK)))
|returns after losing his [[Grimsby (UK Parliament constituency)|Grimsby]] seat at the December 1910 general election.
|-
|[[1911 Bootle by-election]]
|[[Bonar Law]]
| ((Party name with colour|Conservative Party (UK)))
|returns after failing to win [[Manchester North-West (UK Parliament constituency)|Manchester North-West]] in the December 1910 general election.
|-
|[[1908 Dundee by-election]]
|[[Winston Churchill]]
| ((Party name with colour|Liberal Party (UK)))
|returns after losing his [[Manchester North West (UK Parliament constituency)|Manchester North West]] seat in a 1908 by-election, upon his appointment to the [[Board of Trade]].
|-
|[[1906 Dulwich by-election]]
|[[Bonar Law]]
| ((Party name with colour|Conservative Party (UK)))
| returns after losing his [[Glasgow Blackfriars and Hutchesontown (UK Parliament constituency)|Glasgow Blackfriars and Hutchesontown]] seat in the 1906 general election.
|-
|[[February 1906 City of London by-election]]
|[[Arthur Balfour]]
| ((Party name with colour|Conservative Party (UK)))
|returns after losing his [[Manchester East (UK Parliament constituency)|Manchester East]] seat in the 1906 general election.
|}

Notes:

<sup>1</sup> by-election gain lost at the subsequent general election

<sup>2</sup> by-election gain held at the subsequent general election

====Former MPs failing in a by-election====
*[[2022 Birmingham Erdington by-election]]: Former [[Labour Party (UK)|Labour]] MP for [[Coventry South East (UK Parliament constituency)|Coventry South East]] [[Dave Nellist]] stands for the [[Trade Unionist and Socialist Coalition]], coming third with 2.1% of the vote.
*[[2021 Batley and Spen by-election]]: Former [[Glasgow Kelvin (UK Parliament constituency)|Glasgow Kelvin]], [[Bethnal Green and Bow (UK Parliament constituency)|Bethnal Green and Bow]], and [[Bradford West (UK Parliament constituency)|Bradford West]] MP [[George Galloway]], formerly of Labour and then [[Respect Party|Respect]] and now representing the [[Workers Party of Britain]], wins 21% of the vote.
*[[2021 Hartlepool by-election]]: Former [[Stockton South (UK Parliament constituency)|Stockton South]] MP [[Paul Williams (Labour politician)|Paul Williams]], the Labour candidate, lost the seat in the party's greatest-ever reverse while in Opposition.  Former Labour [[Colne Valley (UK Parliament constituency)|Colne Valley]] MP [[Thelma Walker]] also stands as an [[Independent politician|independent]]; and former Labour [[Lancaster and Wyre (UK Parliament constituency)|Lancaster and Wyre]] MP [[Hilton Dawson]] stands for the [[North East Party]]. Neither win more than 1% of the vote.
*[[2019 Brecon and Radnorshire by-election]]: Previous incumbent [[Chris Davies (Conservative politician)|Chris Davies]] runs again after being removed by a recall petition and loses the seat to the Liberal Democrats.
*[[2019 Newport West by-election]]: Former Conservative [[Tatton (UK Parliament constituency)|Tatton]] MP [[Neil Hamilton (politician)|Neil Hamilton]] stands for the [[UK Independence Party]], winning 8.6% of the votes.
*[[2016 Richmond Park by-election]]: Incumbent Richmond Park MP [[Zac Goldsmith]] stands as an independent Conservative to protest against a third runway at Heathrow. He loses to the Liberal Democrats.
*[[2008 Haltemprice and Howden by-election]]: Former [[Vale of Glamorgan (UK Parliament constituency)|Vale of Glamorgan]] MP [[Walter Sweeney (politician)|Walter Sweeney]] stands as an independent, winning 1% of the votes.
*[[2005 Cheadle by-election]]: [[Stephen Day (British politician)|Stephen Day]] fails to regain for the Conservatives a seat he lost by only 33 votes four years previously.
*[[1997 Winchester by-election]]: [[Gerald Malone]] fails to regain the seat for the Conservatives, after losing by only 2 votes six months previously.
*[[1993 Christchurch by-election]]: [[Robert Hayward, Baron Hayward|Robert Hayward]] loses one of the Conservatives' safest seats to the Liberal Democrats.
*[[1990 Eastbourne by-election]]: [[Richard Hickmet]] fails to defend the seat for the Conservatives, after publicly stating that for electors not to support him would be a moral victory for the [[Provisional Irish Republican Army]].
*[[1989 Pontypridd by-election]]: [[Tom Ellis (politician)|Tom Ellis]], former Labour and SDP MP, stands for the [[Liberal Democrats (UK)|Social and Liberal Democrats]], losing his deposit.
*[[1986 Fermanagh and South Tyrone by-election]]: [[Owen Carron]] fails to regain the seat for Sinn Féin that he held 1981–83.
*[[1982 Peckham by-election]]: [[Dick Taverne]], former Labour and Democratic Labour MP, stands for the SDP, fails to take Labour seat.
*[[1982 Gower by-election]]: [[Gwynoro Jones]], former Labour MP, stands for the SDP, fails to take Labour seat.
*[[1982 Beaconsfield by-election]]: [[Paul Tyler]] fails for the Liberals in a by-election held during the [[Falklands War]].
*[[1981 Warrington by-election]]: [[Roy Jenkins]] narrowly fails to win for the SDP from Labour in its first parliamentary contest.
*[[April 1981 Fermanagh and South Tyrone by-election]]: [[Harry West]] fails to regain his old seat against [[Bobby Sands]]
*[[1978 Hamilton by-election]]: [[Margo MacDonald]] fails to repeat the SNP's 1967 triumph.
*[[1978 Ilford North by-election]]: [[Thomas Iremonger]], who had sat for the seat 1954–74, stands as an independent Conservative, winning a mere 1.5% of the vote.
*[[1977 Birmingham Stechford by-election]]: [[Terry Davis (politician)|Terry Davis]] loses a safe Labour seat.
*[[1976 Walsall North by-election]]: [[David Winnick]] loses a safe Labour seat.
*[[1971 Liverpool Scotland by-election]]: [[Peter Mahon (UK politician)|Peter Mahon]] stands as an Independent Labour Anti-Abortion candidate, securing 10.3% of the vote.
*[[1969 Brighton Pavilion by-election]]: [[Thomas Skeffington-Lodge]] stands for Labour in a safe Conservative seat, 19 years after losing his seat.
*[[1967 Nuneaton by-election]]: Air Vice-Marshal [[Don Bennett|Donald Bennett]] stands as a National Party candidate, 22 years after losing his seat as a Liberal MP. 
*[[1965 Salisbury by-election]]: [[Horace Trevor-Cox]] stands as an independent Conservative, 20 years after losing his seat.
*[[1965 Leyton by-election]]: [[Patrick Gordon Walker]] narrowly loses a supposed safe seat.
*[[1962 South Dorset by-election]]: [[Angus Maude]] narrowly loses.
*[[1960 Bolton East by-election]]: [[Frank Byers]] stands for the Liberals.
*[[1956 Hereford by-election]]: [[Frank Owen (politician)|Frank Owen]] fails to regain for the Liberals the seat he previously sat for 1929–1931.
*[[1956 Mid Ulster by-election]]: [[Michael O'Neill (politician)|Michael O'Neill]] fails to regain the seat, a year after retiring as its MP.
*[[1948 Croydon North by-election]]: Air Vice-Marshal [[Don Bennett|Donald Bennett]] stands for the Liberals, losing his deposit, and [[Harold Nicolson]], for Labour, but fail to take a Conservative seat three years after both lost their respective seats.
*[[1941 Hornsey by-election]], [[1941 Hampstead by-election]] and two others: [[Noel Pemberton Billing]] fails to take a seat, 20 years after standing down as an independent MP.
*[[1924 Westminster Abbey by-election]]: [[Winston Churchill]] narrowly fails to take the seat, as a Constitutionalist.
*[[1923 Anglesey by-election]]: [[Edward Thomas John]] failed to defend the seat.
*[[1921 Woolwich East by-election]]: [[Ramsay MacDonald]] loses a supposed safe Labour seat.
*[[1921 Westminster Abbey by-election]]: [[Arnold Lupton]] failed to take a Conservative seat, coming third, ten years after standing down.
*[[1921 Cardiganshire by-election]]: [[W. Llewelyn Williams]] defeated in this race, as anti-Coalition Liberal contesting against a Coalition Liberal, three years after abolition of his previous seat.
*[[1920 Dartford by-election]]: [[Thomas Edward Wing]] failed to defend the seat, over a year after losing his previous seat, losing it to Labour.

=====Re-election of Ministers=====
Until the Re-election of Ministers Acts 1919 and 1926 there were many cases of [[List of ministerial by-elections to the Parliament of the United Kingdom|members having to seek re-election on appointment to ministerial office]]. In eight instances since 1900 they were unsuccessful:
*[[1922 Pontypridd by-election]] [[Thomas Arthur Lewis]] was defeated after being appointed a [[Junior Lord of the Treasury]].
*[[1921 Dudley by-election]] Sir [[Arthur Griffith-Boscawen]] was defeated after being appointed [[Minister of Agriculture, Fisheries and Food|Minister of Agriculture]].
*[[1914 Ipswich by-election]] [[Charles Masterman]] was defeated in a subsequent attempt to return to the House of Commons.
*[[1914 Bethnal Green South West by-election]] [[Charles Masterman]] was defeated after being appointed [[Chancellor of the Duchy of Lancaster]].
*[[1912 Manchester South by-election]] Sir [[Arthur Haworth]] was defeated after being appointed a [[Junior Lord of the Treasury]].
*[[1911 North Ayrshire by-election]] [[Andrew Macbeth Anderson]] was defeated after being appointed [[Solicitor General for Scotland]].
*[[1908 Manchester North West by-election]] [[Winston Churchill]] was defeated after being appointed [[President of the Board of Trade]]
*[[1905 Brighton by-election]] [[Gerald Loder, 1st Baron Wakehurst|Gerald Loder]] was defeated after being appointed [[Lord Commissioner of the Treasury]]

===Shortest-serving by-election victors===
Note this list covers ''completed'' service only; it excludes any current MPs.

====Since 1945====
{| class="wikitable sortable"
|-
!Member of Parliament
!By-election
!colspan=2|Party
!Duration (days)
|-
|[[Bobby Sands]]
|[[April 1981 Fermanagh and South Tyrone by-election|1981 (April) Fermanagh and South Tyrone by-election]]
| ((Party name with colour|Anti H-Block))
|25<sup>1</sup>
|-
|[[Michael Carr (Labour politician)|Michael Carr]]
|[[1990 Bootle by-elections#May by-election|1990 (May) Bootle by-election]]
| ((Party name with colour|rowspan=2|Labour Party (UK)))
|57<sup>1</sup>
|-
|[[Oswald O'Brien]]
|[[1983 Darlington by-election]]
|77<sup>2</sup>
|-
|[[Margo MacDonald]]
|[[1973 Glasgow Govan by-election]]
| ((Party name with colour|Scottish National Party))
|92<sup>2</sup>
|-
|[[Jane Dodds]]
|[[2019 Brecon and Radnorshire by-election]]
| ((Party name with colour|Liberal Democrats (UK)))
|97<sup>2</sup>
|-
|[[Charles Beattie]]
|[[1955 Mid Ulster by-election]]
| ((Party name with colour|Ulster Unionist Party))
|123<sup>3</sup>
|-
|[[Mark Reckless]]
|[[2014 Rochester and Strood by-election]]
| ((Party name with colour|United Kingdom Independence Party))
|130<sup>2b</sup>
|-
|[[Lisa Forbes (politician)|Lisa Forbes]]
|[[2019 Peterborough by-election]]
| ((Party name with colour|Labour Party (UK)))
|153<sup>2</sup>
|-
|[[Sarah Olney]]
|[[2016 Richmond Park by-election]]
| ((Party name with colour|rowspan=2|Liberal Democrats (UK)))
|153<sup>2a</sup>
|-
|[[Nicol Stephen]]
|[[1991 Kincardine and Deeside by-election]]
|154<sup>2</sup>
|-
|[[Ashok Kumar (British politician)|Ashok Kumar]]
|[[1991 Langbaurgh by-election]]
| ((Party name with colour|rowspan=2|Labour Party (UK)))
|154<sup>2a</sup>
|-
|[[Helen McElhone]]
|[[1982 Glasgow Queen's Park by-election]]
|189<sup>4</sup>
|-
|[[David Austick]]
|[[1973 Ripon by-election]]
| ((Party name with colour|Liberal Party (UK)))
|217<sup>2</sup>
|-
|[[John Spellar]]
|[[1982 Birmingham Northfield by-election]]
| ((Party name with colour|Labour Party (UK)))
|224<sup>2a</sup>
|-
|[[Christopher Ward (British politician)|Christopher Ward]]
|[[1969 Swindon by-election]]
| ((Party name with colour|Conservative Party (UK)))
|231<sup>2</sup>
|-
|[[William McCrea, Baron McCrea of Magherafelt and Cookstown|William McCrea]]
|[[2000 South Antrim by-election]]
| ((Party name with colour|Democratic Unionist Party))
|259<sup>2ab</sup>
|-
|[[Parmjit Singh Gill]]
|[[2004 Leicester South by-election]]
| ((Party name with colour|Liberal Democrats (UK)))
|294<sup>2</sup>
|-
|[[David Colville Anderson]]
|[[1963 Dumfriesshire by-election]]
| ((Party name with colour|Unionist Party (Scotland)))
|309<sup>5</sup>
|-
|[[Huw Edwards (politician)|Huw Edwards]]
|[[1991 Monmouth by-election]]
| ((Party name with colour|Labour Party (UK)))
|329<sup>2a</sup>
|-
|[[Thomas Teevan (Unionist politician)|Thomas Teevan]]
|[[1950 Belfast West by-election]]
| ((Party name with colour|Ulster Unionist Party))
|330<sup>2</sup>
|-
|[[Wallace Lawler]]
|[[1969 Birmingham Ladywood by-election]]
| ((Party name with colour|Liberal Party (UK)))
|357<sup>2</sup>
|-
|[[George Machin]]
|[[1973 Dundee East by-election]]
| ((Party name with colour|Labour Party (UK)))
|364<sup>2</sup>
|} 
 
Notes 
*<sup>1</sup> died
*<sup>2</sup> defeated at next general election
*<sup>3</sup> disqualified (Beattie was never elected. He was awarded the seat on the disqualification of his predecessor, only to be found to be disqualified himself)
*<sup>4</sup> retired at next general election (seat abolished by redistribution and failed to secure alternative seat)
*<sup>5</sup> retired at next general election due to personal difficulties
*<sup>a</sup> returned to Parliament at a subsequent election
*<sup>b</sup> had served previously as an MP

====Pre-1945====
*[[Henry Francis Compton]], Conservative [[1905 New Forest by-election]] 46 days <sup>2</sup>
*[[Ronald Bell (UK politician)|Ronald Bell]], Conservative [[1945 Newport by-election]] 70 days <sup>2a</sup>
*[[Don Bennett|Donald Bennett]], Liberal [[1945 Middlesbrough West by-election]] 73 days <sup>2</sup>
*[[John Dumphreys]], Conservative [[1909 Bermondsey by-election]] 83 days <sup>2</sup>
*[[Seaborne Davies]], Liberal [[1945 Caernarvon Boroughs by-election]] 91 days <sup>2</sup>
*[[Ruth Dalton]], Labour [[1929 Bishop Auckland by-election]] 92 days <sup>3</sup>
*[[Joseph Andrews (British politician)|Joseph Ormond Andrews]], Liberal [[1905 Barkston Ash by-election]] 97 days <sup>2</sup>
*Dr [[Robert McIntyre (politician)|Robert McIntyre]], SNP [[1945 Motherwell by-election]] 104 days <sup>2</sup>
*[[George Knox Anderson]], Conservative [[1918 Canterbury by-election]] 113 days <sup>3</sup>
*[[Herbert Evans (politician)|Herbert Evans]], Labour [[1931 Gateshead by-election]] 121 days <sup>1</sup>
*[[Andrew Bathgate Clarke|Andrew Clarke]], Labour [[1929 Midlothian and Peebles Northern by-election]] 121 days <sup>2b</sup>
*Sir [[Sir Henry Wilson, 1st Baronet|Henry Wilson]], Unionist [[February 1922 North Down by-election]] 121 days <sup>5</sup>
*[[Joseph Henderson, 1st Baron Henderson of Ardwick|Joseph Henderson]], Labour [[1931 Manchester Ardwick by-election]] 135 days <sup>2a</sup>
*[[Evan Cotton]], Liberal [[1918 Finsbury East by-election]] 151 days <sup>2</sup>
*[[David Hardie (politician)|David Hardie]], Labour [[1931 Rutherglen by-election]] 159 days <sup>2</sup>
*[[Lord Arthur Hill]], Unionist [[1907 West Down by-election]] 193 days <sup>7b</sup>
*[[Oswald Cawley]], Liberal [[January 1918 Prestwich by-election]] 202 days <sup>1</sup>
*[[Francis Norie-Miller]], Liberal National [[1935 Perth by-election]] 212 days <sup>3</sup>
*[[George Banton]], Labour [[1922 Leicester East by-election]] 230 days <sup>2a</sup>
*[[William Henry Somervell]], Liberal [[1918 Keighley by-election]] 232 days <sup>2</sup>
*[[Noel Noel-Buxton, 1st Baron Noel-Buxton|Noel Edward Buxton]], Liberal [[1905 Whitby by-election]] 238 days <sup>2a</sup>
*[[Leslie Orme Wilson]], Conservative [[1922 Portsmouth South by-election]] 243 days <sup>7b</sup>
*[[Leah Manning]], Labour [[1931 Islington East by-election]] 250 days <sup>2a</sup>
*[[Frederick William Gibbins]], Liberal [[1910 Mid Glamorgan by-election]] 253 days <sup>3</sup>
*[[Charles Frederick Palmer|C. V. F. Palmer]], Independent Conservative [[February 1920 The Wrekin by-election]] 261 days <sup>1</sup>
*[[Maurice Healy]], Ind. Nationalist [[1909 Cork City by-election]] 262 days <sup>2ab</sup>
*[[John Edward Sutton]], Labour [[1922 Manchester Clayton by-election]] 270 days <sup>2ab</sup>
*[[James Chuter Ede]], Labour [[1923 Mitcham by-election]] 278 days <sup>2a</sup>
*[[J. J. Cleary]], Labour [[1935 Liverpool Wavertree by-election]] 281 days <sup>2</sup>
*Sir [[William Beveridge]], Liberal [[1944 Berwick-upon-Tweed by-election]] 282 days <sup>2</sup>
*[[W. P. Sidney]], Conservative [[1944 Chelsea by-election]] 288 days <sup>4</sup>
*Sir [[John Reith, 1st Baron Reith|John Reith]], [[National Government (United Kingdom)|National]] [[February 1940 Southampton by-election]] 293 days <sup>6</sup>
*[[W. E. Gibbons]], Conservative [[1944 Bilston by-election]] 309 days <sup>2</sup>
*[[Lord Charles Beresford]], Conservative [[1902 Woolwich by-election]] 320 days <sup>7ab</sup>
*[[Arthur Henderson]], Labour [[1923 Newcastle-upon-Tyne East by-election]] 323 days <sup>2ab</sup>
*[[James Henry Hall]], Labour [[1930 Whitechapel and St Georges by-election]] 328 days <sup>2a</sup>
*[[Thomas Naylor (UK politician)|Thomas Naylor]], Labour [[1921 Southwark South East by-election]] 336 days <sup>2a</sup>

:<sup>1</sup> died
:<sup>2</sup> defeated at next general election
:<sup>3</sup> retired at next general election
:<sup>4</sup> retired at next general election, upon succession to a peerage
:<sup>5</sup> assassinated by IRA
:<sup>6</sup> elevated to the Peerage
:<sup>7</sup> resigned
:<sup>a</sup> returned to Parliament at a subsequent election
:<sup>b</sup> had served previously as an MP

===Youngest by-election victors===
* [[Esmond Harmsworth, 2nd Viscount Rothermere|Esmond Harmsworth]], elected on 15 November 1919 from [[Isle of Thanet (UK Parliament constituency)|Isle of Thanet]] aged 21 years 170 days.<ref>Since the [[Reform Act 1832]]; of those whose age can be verified.</ref>
* Youngest woman: [[Bernadette Devlin McAliskey|Bernadette Devlin]], elected on 17 April 1969 from [[Mid Ulster (UK Parliament constituency)|Mid Ulster]] aged 21 years 359 days.

====Babies of the House elected at by-elections====

''See'' [[Baby of the House of Commons]]

===Oldest by-election victors===

Debuts in Parliament:

*[[John Benbow (MP)|John Benbow]] was 75 or 76 when he held the [[1844 Dudley by-election]] for the Conservatives.
*[[Hucks Gibbs, 1st Baron Aldenham|Hucks Gibbs]] was 71 when he held the [[April 1891 City of London by-election]] for the Conservatives.
*[[Philip Manfield]] was 71 or 72 when he held the [[1891 Northampton by-election]] for the Liberals.
*Sir [[Robert Pullar]] was 79 (less 6 days) when he held the [[1907 Perth by-election]] for the Liberals.
*[[David Cleghorn Hogg]] was 73 when he gained the [[1913 Londonderry City by-election]] for the Liberals.
*[[Swire Smith|Sir Swire Smith]] was 73 when he held the [[1915 Keighley by-election]] for the Liberals.
*[[William Frederick Hicks Beach]] was 74 when he held the [[1916 Tewkesbury by-election]] for the Conservatives.
*Sir [[George Reid]] was 70 when he held the [[1916 St George's, Hanover Square by-election]] for the Conservatives. He was a former Prime Minister of Australia.
*Sir [[John Fleming (Scottish politician)|John Fleming]] was 69 or 70 when he held the [[1917 Aberdeen South by-election]] for the Liberals.
*[[George Edwards (UK politician)|George Edwards]] was almost 70 when he gained the [[1920 South Norfolk by-election]] for Labour. He was a former agricultural labourer.
*[[Henry Bruce Armstrong]] was almost 77 when he held the [[1921 Mid Armagh by-election]] for the Ulster Unionists.
*[[William Nathaniel Jones]] was 70 when he held the [[1928 Carmarthen by-election]] for the Liberals.
*[[Francis Norie-Miller]] was 76 when he gained the [[1935 Perth by-election]] for the Liberal Nationals.
*[[James Little (British politician)|James Little]] was 70 when he held the [[1939 Down by-election]] for the Ulster Unionists.
*[[John Evans (Ogmore MP)|John Evans]] was 70 when he held the [[1946 Ogmore by-election]] for Labour.

Comebacks to Parliament:

*[[John Blaquiere, 1st Baron de Blaquiere|John Blaquiere]] was 71 when he held the [[June 1803 Downton by-election]] for the Tories. He was previously MP for [[Rye (UK Parliament constituency)|Rye]] in 1801–02.
*[[Bartholomew Bouverie]] was 73 when he held the [[1826 Downton by-election]] for the Tories. He was previously MP for the same seat from 1819 until the [[United Kingdom general election|general election earlier in 1826]].
*[[Quintin Dick]] was 71 when he held the [[1848 Aylesbury by-election]] for the Conservatives. He was previously MP for [[Maldon (UK Parliament constituency)|Maldon]] in 1830–47.
*[[James William Freshfield]] was 77 when he won the [[1851 Boston by-election]] for the Conservatives. He was previously MP for [[Penryn and Falmouth (UK Parliament constituency)|Penryn and Falmouth]] in 1835–41.
*[[William Johnson Fox]] was 71 when he held the [[1857 Oldham by-election]] for the Liberals. He was previously MP for the same seat from 1852 until the [[1857 United Kingdom general election|general election]] earlier in 1857.
*[[William Cubitt (politician)|William Cubitt]] was 71 when he held the [[1862 Andover by-election]] for the Conservatives. He was previously MP for the same seat in 1847–61.
*[[John Morgan Cobbett]] was 71 when he won the [[1872 Oldham by-election]] for the Conservatives. He had been previously MP for the same seat as a Liberal in 1852–65.
*[[James Patrick Mahon]] was 79 when he held the [[1879 Clare by-election]] and 87 when he held the [[1887 County Carlow by-election]] for the Irish Nationalists.
*[[Isaac Holden]] was 75 when he held the [[1882 West Riding of Yorkshire by-election]] for the Liberals. He had previously been MP for [[Knaresborough (UK Parliament constituency)|Knaresborough]] in 1865–68.
*[[Sir Wilfrid Lawson, 2nd Baronet, of Brayton|Sir Wilfrid Lawson]] was 74 when he held the [[1903 Camborne by-election]] for the Liberals. He had previously been MP for [[Cockermouth (UK Parliament constituency)|Cockermouth]] in 1886–1900.
*[[John Frederick Cheetham]] was 70 when he won the [[1905 Stalybridge by-election]] for the Liberals. He had served previously as MP for [[North Derbyshire (UK Parliament constituency)|North Derbyshire]] 1880-85 prior to that seat's abolition.
*[[Alfred Hopkinson|Sir Alfred Hopkinson]] was 74 when he won the [[1926 Combined English Universities by-election]] for the Conservatives. He had previously been MP for [[Cricklade (UK Parliament constituency)|Cricklade]] 1895-98 before resigning.
*[[Arthur Salter, 1st Baron Salter|Arthur Salter]] was 70 when he held the [[1951 Ormskirk by-election]] for the Conservatives. He had served previously as MP for [[Oxford University (UK Parliament constituency)|Oxford University]] 1937-50 prior to that seat's abolition.

In defence of a previously held seat:

*[[Enoch Powell]] was 73 when he successfully defended his seat at the [[1986 South Down by-election]] for the Ulster Unionists, after a protest resignation against the [[Anglo-Irish Agreement]], although he had been an MP almost continuously since 1950.

===First women by-election victors===
The first woman to be elected in a by-election was [[Nancy Astor]], who succeeded her husband at the [[1919 Plymouth Sutton by-election]], becoming the first woman to take her seat in the House of Commons.

The first woman to gain a seat in a by-election was [[Susan Lawrence]] who won the [[1926 East Ham North by-election]], although she had previously sat for the same seat between 1923 and 1924.<sup>1</sup>

The first woman to gain a seat ''ab initio'' in a by-election was [[Jennie Lee, Baroness Lee of Asheridge|Jennie Lee]] who won the [[1929 North Lanarkshire by-election]], at the same time becoming the first woman [[Baby of the House|Baby of the House of Commons]].

Note
<sup>1</sup> [[Mabel Philipson]] succeeded her husband at the [[1923 Berwick-upon-Tweed by-election]]. He had been elected as a [[National Liberal Party (UK, 1922)|National Liberal Party]] candidate. She won as a [[Conservative Party (UK)|Conservative]] so this could arguably be classed as the first gain by a woman.

===First ethnic minority by-election victors===
Whilst the first ethnic minority Members of Parliament were elected at general elections as early as the 1890s, it would be almost 100 years before one was returned at a by-election.

The first ethnic minority candidate to be elected in a by-election was [[Ashok Kumar (UK politician)|Ashok Kumar]] who gained the [[1991 Langbaurgh by-election]] for Labour.

*[[David Lammy]] held the [[2000 Tottenham by-election]] for Labour.
*[[Mark Hendrick]] held the [[2000 Preston by-election]] for Labour.
*[[Parmjit Singh Gill]] gained the [[2004 Leicester South by-election]] for the Liberal Democrats.
*[[Seema Malhotra]] held the [[2011 Feltham and Heston by-election]] for Labour, the first woman to win it.

The first by-election in which all three major-party candidates were from the ethnic minorities was the [[2007 Ealing Southall by-election]], held by Labour.

===First by-election victors from specific religions===
When the UK Parliament was established in 1801, non-Anglicans were prevented from taking their seats as MPs under the [[Test Act 1672]]. However, [[Methodist]]s took communion at Anglican churches until 1795, and some continued to do so, and many [[Presbyterian]]s were prepared to accept Anglican communion, thus ensuring that members of these creeds were represented in the Parliament.<ref>Chris Pond, [http://www.parliament.uk/commons/lib/research/notes/snpc-01493.pdf Parliament and Religious Disabilities] ((webarchive |url=https://web.archive.org/web/20070928094928/http://www.parliament.uk/commons/lib/research/notes/snpc-01493.pdf |date=September 28, 2007 ))</ref> Some [[Unitarianism|Unitarians]] were also elected.

The first by-election victor (and first ever MP) to be an adherent of the [[Eastern Orthodox Church]] was [[Frederick North, 5th Earl of Guilford|The Honourable Frederick North]] who was elected in 1792 for [[Banbury (UK Parliament constituency)|Banbury]] (to succeed his brother who had entered the House of Lords), having converted to the faith the previous year.

The first [[Roman Catholic]] by-election victor in the UK Parliament was [[Daniel O'Connell]] in the [[1828 Clare by-election]]. He was not permitted to take his seat until the following year.

The first [[atheist]] by-election victor was [[Charles Bradlaugh]], at the [[1881 Northampton by-election]]. As an atheist, Bradlaugh was not allowed to swear the [[Oath of Allegiance (United Kingdom)|Oath of Allegiance]], and the by-election was re-run in [[1882 Northampton by-election|1882]] and [[1884 Northampton by-election|1884]]. Both were also won by Bradlaugh, who eventually was able to take his seat after the [[1885 United Kingdom general election|1885 general election]].<ref>((cite news|url=http://www.john-clarke.co.uk/bradlaugh.html|title=Charles Bradlaugh|author=John M. Clarke|newspaper=Necropolis News|date=November 1993|access-date=20 April 2017))</ref>

* [[David Salomons]] was the first [[Jewish]] by-election victor, at the [[1851 Greenwich by-election]].
* [[Terry Rooney (politician)|Terry Rooney]] was the first [[Mormon]] by-election victor, at the [[1990 Bradford North by-election]].
* [[Parmjit Singh Gill]] became the first [[Sikh]] by-election victor, at the [[2004 Leicester South by-election]].
* [[Virendra Sharma]] became the first [[Hindu]] by-election victor, at the [[2007 Ealing Southall by-election]].
* [[Rosena Allin-Khan]] was the first [[Muslim]] by-election victor, at the [[2016 Tooting by-election]].

===Physically disabled by-election victors===
Most physically disabled MPs in the history of the parliament entered in the intakes of general elections. Those known to have been disabled when entering parliament at by-elections are rarer and include:

*[[John Horne Tooke]], who lost sight of an eye in a boyhood fight, won the [[1801 Old Sarum by-election]].
*[[Fulk Greville Howard]], who lost sight of an eye in the [[Helder expedition]] in 1799, won the [[1808 Castle Rising by-election]]. 
*[[William Beresford, 1st Viscount Beresford|Sir William Carr Beresford]], who lost sight of an eye in an accident on military service in 1786, won the [[1811 County Waterford by-election]].
*[[Samuel Shepherd]], increasingly deaf from 1790, won the [[1814 Dorchester by-election]].
*[[Arthur MacMurrough Kavanagh]], born without hands and feet, won the [[1866 Wicklow County by-election]].
*[[Michael Davitt]], who lost his right arm in a factory accident in 1857, won the [[1882 Meath by-election]], although he was disqualified from sitting because he was in prison.
*[[Aubrey Herbert]], who was almost blind from childhood, won the [[1911 South Somerset by-election]].
*[[Mabel Philipson]], who lost sight in one eye after a car crash in 1911, who won the [[1923 Berwick-upon-Tweed by-election]].<ref>((cite news|title=Stanley Rhodes Dies|url=https://timesmachine.nytimes.com/timesmachine/1911/08/17/105031393.pdf|access-date=7 August 2015|work=New York Times|date=17 August 1911))</ref><ref name="portrait">((cite book |last1=Ball |first1=Stuart |author-link = Stuart Ball |title=Portrait of a Party: The Conservative Party in Britain 1918–1945 |date=2013 |publisher=OUP |location=Oxford |isbn=9780191644832 |page=324 |url=https://books.google.com/books?id=whBpAgAAQBAJ))</ref>
*[[John Dugdale (Labour politician)|John Dugdale]], who was partly deaf from childhood, won the [[1941 West Bromwich by-election]].
*[[Violet Bathurst, Lady Apsley]], who was left permanently disabled and unable to walk by a hunting accident in 1930, won the [[1943 Bristol Central by-election]], <ref>((cite news |url=https://thebristolcable.org/2020/01/the-tale-of-bristols-fascist-sympathising-disability-rights-promoting-first-woman-mp/ |title=The tale of Bristol's fascist-sympathising, disability rights-promoting first woman MP |last=Dresser |first=Madge |website=The Bristol Cable |date=6 January 2020))</ref>
*[[Cecil Manning]], who lost his right arm in action in [[World War I]], won the [[1944 Camberwell North by-election]].
*[[Hervey Rhodes, Baron Rhodes|Hervey Rhodes]], who walked with a limp since severe wounding in World War I, won the [[1945 Ashton-under-Lyne by-election]].
*[[William Rees-Davies (Conservative politician)|William Rees-Davies]], who lost his right arm in action in [[World War II]], won the [[1953 Isle of Thanet by-election]].

===By-elections losers awarded seats on disqualification of winner===
*[[Malcolm St. Clair (UK politician)|Malcolm St Clair]], [[1961 Bristol South East by-election]] (resigned in 1963 to enable [[1963 Bristol South East by-election|another by-election]])
*[[Charles Beattie]], [[1955 Mid Ulster by-election]] (he too was disqualified a few weeks later, causing [[1956 Mid Ulster by-election|another by-election]])
*Pre-1945: [[Stephen Moore (MP)|Stephen Moore]], [[March 1875 Tipperary by-election]] (retired in [[1880 United Kingdom general election in Ireland|1880]])

=== Two or more former MPs contest by-election ===
* [[2021 Hartlepool by-election]]<sup>1</sup> (three former MPs)
* [[2008 Haltemprice and Howden by-election]]<sup>2</sup>
* [[1997 Winchester by-election]]
* [[1986 Fermanagh and South Tyrone by-election]]
* [[1982 Beaconsfield by-election]]
* [[1981 Warrington by-election]]
* [[1969 Brighton Pavilion by-election]]
* [[1965 Salisbury by-election]]
* [[1956 Mid Ulster by-election]]
* [[1948 Croydon North by-election]]
* [[1933 Altrincham by-election]] (three former MPs)
* [[1930 Glasgow Shettleston by-election]]
* [[1930 Nottingham Central by-election]] (three former MPs)
* [[1928 Cheltenham by-election]]

<sup>1</sup>Hilton Dawson, Thelma Walker, and Paul Williams
<sup>2</sup> Conservative MPs David Davis and Walter Sweeney

==Frequency and duration records==

===Longest period without a by-election===
The years 1998 and 2020 stand as the two in modern British history without any Westminster election. 1992, 1998, 2010 and 2020 are the four full calendar years in history without a single by-election.

{| class=wikitable
|-
!From
!To
!Period (days)
|-
|1 August 2019
|6 May 2021
|645
|-
|20 November 1997
|10 June 1999
|567
|-
|7 November 1991
|6 May 1993
|546
|-
|12 March 1987
|14 July 1988
|489
|-
|14 February 2002
|18 June 2003
|483
|-
|23 February 2017
|3 May 2018
|434
|-
|12 November 2009
|13 January 2011
|427
|-
|23 May 1974
|26 June 1975
|399
|-
|18 June 2003
|15 July 2004
|393
|-
|29 June 2006
|19 July 2007
|385
|}

===Longest period between a vacancy arising and a by-election writ being moved===
*[[1941 The Wrekin by-election]]: 357 days. [[James Baldwin-Webb]] was presumed killed as a result of enemy action when [[SS City of Benares]] was torpedoed on 17 September 1940; the writ was moved on 9 September 1941.
*[[1941 King's Norton by-election]]: 327 days. [[Ronald Cartland]] was killed in action on 29–30 May 1940. Initially posted missing, his death was not presumed until January 1941. The writ was moved on 22 April 1941.
*[[1941 Hitchin by-election]]: 272 days. Sir [[Arnold Wilson]] was presumed killed in action on 31 May 1940; the writ was moved on 27 February 1941.
*[[1969 Newcastle-under-Lyme by-election]]: 236 days. [[Stephen Swingler]] died on 19 February 1969; the writ was moved on 13 October 1969.
*[[1969 Swindon by-election]]: 220 days. [[Francis Noel-Baker]] resigned on 7 March 1969; the writ was moved on 13 October 1969.

===Longest period without a seat changing hands===
The longest period without a seat changing hands in a by-election was the five years between the Conservative victories in the [[1948 Glasgow Camlachie by-election]] and the [[1953 Sunderland South by-election]].

During the short Parliaments of 1910, 1950-1 and 1974 no seats changed hands in a by-election.

===Longest period between by-election gains for a party===
The Liberal Party endured 29 years without a single by-election gain between the [[1929 Holland with Boston by-election]] and the [[1958 Torrington by-election]]. It did not win a single by-election in the thirteen years between holding the [[1945 Middlesbrough West by-election]] and gaining Torrington.

Until the [[2008 Crewe and Nantwich by-election]], the opposition Conservative Party had not gained a seat in almost 26 years, the last being the [[1982 Mitcham and Morden by-election]], which occurred during the unique circumstances of the [[Falklands War]] and the sitting Labour MP defecting to the Social Democratic Party and seeking re-election under his new party label. The Conservatives' last gain while in Opposition was 30 years previously at the [[1978 Ilford North by-election]].

Labour's longest lean stretch was almost 18 years, between gaining the [[1939 Brecon and Radnorshire by-election]] and the [[1957 Lewisham North by-election]].<sup>1</sup>

As of ((Date)), the most recent gains for each currently active party were:

{| class="wikitable"
|-
!! scope="col" colspan=2 | Party 
!! scope="col" | Date
!! scope="col" | Time since
!! scope="col" | By-election
!! scope="col" colspan=3 | Result
|-
| ((Party name with colour|Labour Party (UK)))
| 19 October 2023
| ((Age in years, months and days|2023|10|19))
| [[2023 Tamworth by-election|Tamworth]]<br />[[2023 Mid Bedfordshire by-election|Mid Bedfordshire]]
| Gain from
| ((Party name with colour|Conservative Party))
|-
| ((Party name with colour|Liberal Democrats (UK)))
| 20 July 2023
| ((Age in years, months and days|2023|07|20))
| [[2023 Somerton and Frome by-election|Somerton and Frome]]
| Gain from
|((Party name with colour|Conservative Party (UK)))
|-
| ((Party name with colour|Conservative Party (UK)))
| 6 May 2021
| ((Age in years, months and days|2021|05|06))
| [[2021 Hartlepool by-election|Hartlepool]]
| Gain from
| ((Party name with colour|Labour Party (UK)))
|-
| ((Party name with colour|UKIP))
| 20 November 2014
| ((Age in years, months and days|2014|11|20))
| [[2014 Rochester and Strood by-election|Rochester and Strood]]<sup>2</sup>
| Gain from
| ((Party name with colour|Conservative Party (UK)))
|-
| ((Party name with colour|Scottish National Party))
| 24 July 2008
| ((Age in years, months and days|2008|07|24))
| [[2008 Glasgow East by-election|Glasgow East]]
| Gain from
| ((Party name with colour|Labour Party (UK)))
|-
| ((Party name with colour|Democratic Unionist Party))
| 27 April 2000
| ((Age in years, months and days|2000|04|27))
| [[2000 South Antrim by-election|South Antrim]]
| Gain from
|  ((Party name with colour|rowspan=2|Ulster Unionist Party))
|-
| ((Party name with colour|Social Democratic and Labour Party))
| 23 January 1986
| ((Age in years, months and days|1986|01|23))
| [[1986 Newry and Armagh by-election|Newry and Armagh]]
| Gain from
|-
| ((Party name with colour|Plaid Cymru))
| 14 July 1966
| ((Age in years, months and days|1966|07|14))
| [[1966 Carmarthen by-election|Carmarthen]]
| Gain from
| ((Party name with colour|Labour Party (UK)))
|-
| ((Party name with colour|Ulster Unionist Party))
| 6 June 1946
| ((Age in years, months and days|1946|06|06))
| [[1946 Down by-election|Down]]<sup>3</sup>
| Gain from
| ((Party name with colour|Independent Unionist))
|-
| ((Party name with colour|Sinn Féin))
| 20 June 1918
| ((Age in years, months and days|1918|06|20))
| [[1918 East Cavan by-election|East Cavan]]<sup>4</sup>
| Gain from
| ((Party name with colour|Irish Parliamentary Party))
|}
Notes
<sup>1</sup> The Labour Party were the official opposition in the Parliament elected in 1935, but after the major parties agreed an electoral truce on the outbreak of war in 1939, they did not contest any Conservative or Liberal seats for the remainder of the Parliament, a period of six years, and were members of the [[Churchill war ministry|wartime coalition government]] between May 1940 and May 1945.<br />
<sup>2</sup> Notional gain: incumbent Conservative stood as UKIP. No UKIP candidate has ever defeated an incumbent of a different party<br />
<sup>3</sup> The UUP were also declared winners of the [[1955 Mid Ulster by-election]] after the Sinn Féin candidate was disqualified, but the UUP candidate was also disqualified shortly after.<br />
<sup>4</sup> Sinn Féin have not gained a seat at a by-election since 1918. However, the [[Anti H-Block]] party, an Irish Republican group that merged into Sinn Féin, gained [[Fermanagh and South Tyrone (UK Parliament constituency)|Fermanagh and South Tyrone]] in the [[April 1981 Fermanagh and South Tyrone by-election|April 1981 by-election]] (((Age in years, months and days|1981|04|09)) ago).

===Longest period between by-election holds for a party===
The Conservatives did not successfully defend a single by-election in the eight years between their holds of the [[1989 Richmond (Yorks) by-election]] and the [[1997 Uxbridge by-election]], losing a record 15 consecutive seats where they were the incumbents. By the time of the by-election in Uxbridge, the victor in Richmond, [[William Hague]], had become leader of the Conservative Party.

Labour's worst run was 4 consecutive by-election losses, which has occurred three times since 1945:

* between holding the [[1976 Newcastle-upon-Tyne Central by-election]] and the [[1977 Grimsby by-election]].
* between holding the [[1967 Manchester Gorton by-election]] and the [[1968 Sheffield Brightside by-election]].
* between holding the [[1967 Rhondda West by-election]] and the [[1967 Manchester Gorton by-election]].

===Longest period between by-election losses for a party===
Between the [[1988 Glasgow Govan by-election]] and the [[2003 Brent East by-election]], Labour successfully defended every seat it held at by-elections, for a total of 30 holds (not counting [[2000 Falkirk West by-election|Falkirk West]] and [[2000 West Bromwich West by-election|West Bromwich West]], represented by a Labour MP turned independent and a Labour speaker respectively and both won by Labour). The span of ((Age in years, months and days|1988|11|10|2003|09|18)) is the longest period without a by-election defeat for either of the two main parties. The Conservatives did not lose a seat between the [[2000 Romsey by-election]] and the [[2012 Corby by-election]], a span of ((Age in years, months and days|2000|05|03|2012|11|15)). However, they only defended 3 seats in that time. In terms of total number, their longest run of by-election holds was 51, between the [[1945 Chelmsford by-election]] and the [[1957 Lewisham North by-election]], a span of ((Age in years, months and days|1945|04|24|1957|02|14)).

Since their formation, the Liberal Democrats have held every Lib Dem seat contested at a by-election, of which there have been 3. Including their successor parties, their most recent by-election loss was the [[1982 Mitcham and Morden by-election]], lost by the SDP ((Age in years, months and days|1982|06|03)) ago. The SDP candidate had however defected from Labour – the last seat lost by either party that had been won at a previous election was the [[1957 Carmarthen by-election]], lost by the Liberals ((Age in years, months and days|1957|02|28)) ago. Since 1982, the Liberal Democrats and predecessors together have defended 4; since 1957 they have defended 5 seats.

By-elections in seats held by minor and nationalist parties are rare, and so most have never lost a seat. The SNP lost their first seat at the [[2023 Rutherglen and Hamilton West by-election]]. The DUP and Plaid Cymru have defended but never lost a seat at a by-election, Sinn Féin have only lost seats by disqualification, and the UUP have never lost more than one seat in a row. No by-election has ever been called in an SDLP held seat.

===Longest period without an opposition gain===
For a period of 11 years, from the 1997 general election until the [[2008 Crewe and Nantwich by-election]], the principal opposition Conservative Party failed to register a by-election gain against the incumbent Labour Government. This is the longest period of such failure since records began, and more than twice the previous record of the five years it took the then Labour opposition to gain the [[1957 Lewisham North by-election]]. Labour did however lose 3 seats to the Liberal Democrats in that period, their first being the [[2003 Brent East by-election]].

The present Labour opposition did not register a gain for over nine years, between the [[2012 Corby by-election]] and the [[2022 Wakefield by-election]]. In this period, the Conservative government lost three seats in by-elections where the former Conservative incumbent stood for a different party ([[2014 Clacton by-election]] and [[2014 Rochester and Strood by-election]], both lost to UKIP) or as an independent ([[2016 Richmond Park by-election]], lost to the Liberal Democrats). Their first loss in a by-election without a sitting incumbent was to the Liberal Democrats at the [[2019 Brecon and Radnorshire by-election]].

Apart from the brief parliaments of 1910, 1950-1 and 1974, the parliaments of 1951-5 and 1997-2001 are the only occasions when the Government did not lose a by-election.

===Most by-elections in one day===
The largest number of by-elections held on a single day occurred on 23 January 1986 when [[1986 Northern Ireland by-elections|15 simultaneous contests were held in Northern Ireland]]. The elections had been engineered by the incumbent Unionist parties as a protest against the [[Anglo-Irish Agreement]] of 1985. They intended the results to be interpreted as a referendum on the treaty. The elections were boycotted by the main Nationalist parties except in four seats where they had a reasonable prospect of victory. In the event, the [[Social Democratic and Labour Party]] gained one seat, [[Newry and Armagh (UK Parliament constituency)|Newry and Armagh]], from the [[Ulster Unionist Party]].

Apart from the above example, it is common for UK mainland parties to schedule several by-elections on the same day. Motivations include attempting to divide opponents' resources and getting bad news (expected losses) out of the way. Since 1945, the largest number of simultaneous mainland by-elections has been 6, held on 16 November 1960. On four occasions, 5 by-elections have been held on the same day, most recently on 9 June 1994. Groupings of two or three are very common.

Before November 2012, the last day on which three by-elections had been held was 23 November 2000. In November 2012 there were two such groupings of three (15 November and 29 November). The last time there were six by-elections in one calendar month was in June 1994.

===Most by-election losses in one day===
The largest number of by-elections lost on a single day is three, when the Labour party lost [[1968 Acton by-election|Acton]], [[1968 Dudley by-election|Dudley]] and [[1968 Meriden by-election|Meriden]] on 28 March 1968, all to the Conservatives.

Occasions since 1945 when two seats have fallen are:

{| class="wikitable"
|-
!Date
!By-election
!colspan=2|Winning party
!colspan=4|Losing party
|-
| rowspan="2"|19 October 2023
| [[2023 Tamworth by-election]]
| ((Party name with colour|rowspan=2|Labour Party (UK)))
| ((Party name with colour|rowspan=8|Conservative Party (UK)))
|-
| [[2023 Mid Bedfordshire by-election]]
|-
| rowspan="2"|20 July 2023
| [[2023 Somerton and Frome by-election]]
| ((Party name with colour|Liberal Democrats (UK)))
|-
| [[2023 Selby and Ainsty by-election ]]
| ((Party name with colour|Labour Party (UK)))
|-
| rowspan="2"|23 June 2022
| [[2022 Tiverton and Honiton by-election]]
| ((Party name with colour|Liberal Democrats (UK)))
|-
| [[2022 Wakefield by-election]]
| ((Party name with colour|Labour Party (UK)))
|-
| rowspan="2"|7 November 1991
| [[1991 Kincardine and Deeside by-election]]
| ((Party name with colour|Liberal Democrats (UK)))
|-
| [[1991 Langbaurgh by-election]]
| ((Party name with colour|Labour Party (UK)))
|-
| rowspan="2"|4 November 1976
| [[1976 Walsall North by-election]]
| ((Party name with colour|rowspan=2|Conservative Party (UK)))
| ((Party name with colour|rowspan=3|Labour Party (UK)))
|-
| [[1976 Workington by-election]]
|-
| rowspan="2"|8 November 1973
| [[1973 Glasgow Govan by-election]] 
| ((Party name with colour|Scottish National Party))
|-
| [[1973 Berwick-upon-Tweed by-election]]
| ((Party name with colour|rowspan=3|Liberal Party (UK)))
| ((Party name with colour|rowspan=3|Conservative Party (UK)))
|-
| rowspan="2"|26 July 1973
| [[1973 Ripon by-election]]
|-
| [[1973 Isle of Ely by-election]]
|-
| rowspan="2"|2 November 1967
| [[1967 Hamilton by-election]]
| ((Party name with colour|Scottish National Party))
| ((Party name with colour|rowspan=4|Labour Party (UK)))
|-
| [[1967 Leicester South West by-election]]
| ((Party name with colour|rowspan=3|Conservative Party (UK)))
|-
| rowspan="2"|21 September 1967 
| [[1967 Walthamstow West by-election]]
|-
| [[1967 Cambridge by-election]]
|-
| rowspan="2"|22 November 1962
| [[1962 Glasgow Woodside by-election]]
| ((Party name with colour|rowspan=2|Labour Party (UK)))
| ((Party name with colour|rowspan=2|Conservative Party (UK)))
|-
| [[1962 South Dorset by-election]]
|}

===Seats with more than one by-election in a single Parliament===
*[[Bootle (UK Parliament constituency)|Bootle]]: [[1990 Bootle by-elections|May and November 1990]].
*[[Fermanagh and South Tyrone (UK Parliament constituency)|Fermanagh and South Tyrone]]: [[April 1981 Fermanagh and South Tyrone by-election|April]] and [[August 1981 Fermanagh and South Tyrone by-election|August 1981]].
*[[Bristol South East (UK Parliament constituency)|Bristol South East]]: [[1961 Bristol South East by-election|1961]] and [[1963 Bristol South East by-election|1963]].
*[[Mid Ulster (UK Parliament constituency)|Mid Ulster]]: [[1955 Mid Ulster by-election|1955]] and [[1956 Mid Ulster by-election|1956]].
*[[Edinburgh East (UK Parliament constituency)|Edinburgh East]]: [[1945 Edinburgh East by-election|1945]] and [[1947 Edinburgh East by-election|1947]].
*[[Middlesbrough West (UK Parliament constituency)|Middlesbrough West]]: [[1940 Middlesbrough West by-election|1940]] and [[1945 Middlesbrough West by-election|1945]].
*[[Combined Scottish Universities (UK Parliament constituency)|Combined Scottish Universities]]: [[1936 Combined Scottish Universities by-election|1936]], [[1938 Combined Scottish Universities by-election|1938]] and [[1945 Combined Scottish Universities by-election|1945]].
*[[Berwick-upon-Tweed (UK Parliament constituency)|Berwick-upon-Tweed]]: [[1941 Berwick-upon-Tweed by-election|1941]] and [[1944 Berwick-upon-Tweed by-election|1944]].
*[[Clay Cross (UK Parliament constituency)|Clay Cross]]: [[1936 Clay Cross by-election|1936]] and [[1944 Clay Cross by-election|1944]].
*[[West Derbyshire (UK Parliament constituency)|West Derbyshire]]: [[1938 West Derbyshire by-election|1938]] and [[1944 West Derbyshire by-election|1944]].
*[[Buckingham (UK Parliament constituency)|Buckingham]]: [[1937 Buckingham by-election|1937]] and [[1943 Buckingham by-election|1943]].
*[[Manchester Gorton (UK Parliament constituency)|Manchester Gorton]]: [[1937 Manchester Gorton by-election|1937]] and [[1942 Manchester Gorton by-election|1942]].
*[[Dunbartonshire (UK Parliament constituency)|Dunbartonshire]]: [[1936 Dunbartonshire by-election|1936]] and [[1941 Dunbartonshire by-election|1941]].
*[[Greenock (UK Parliament constituency)|Greenock]]: [[1936 Greenock by-election|1936]] and [[1941 Greenock by-election|1941]].
*[[Doncaster (UK Parliament constituency)|Doncaster]]: [[1938 Doncaster by-election|1938]] and [[1941 Doncaster by-election|1941]].
*[[Southampton (UK Parliament constituency)|Southampton]]: [[February 1940 Southampton by-election|February]] and [[November 1940 Southampton by-election|November 1940]].
*[[Preston (UK Parliament constituency)|Preston]]: [[1936 Preston by-election|1936]] and [[1940 Preston by-election|1940]].
*[[Wandsworth Central (UK Parliament constituency)|Wandsworth Central]]: [[1937 Wandsworth Central by-election|1937]] and [[1940 Wandsworth Central by-election|1940]].
*[[City of London (UK Parliament constituency)|City of London]]: [[1938 City of London by-election|1938]] and [[1940 City of London by-election|1940]].
*[[Combined Scottish Universities (UK Parliament constituency)|Combined Scottish Universities]]: [[1934 Combined Scottish Universities by-election|1934]] and [[1935 Combined Scottish Universities by-election|1935]].
*[[Eastbourne (UK Parliament constituency)|Eastbourne]]: [[1932 Eastbourne by-election|1932]] and [[1935 Eastbourne by-election|1935]].
*[[Twickenham (UK Parliament constituency)|Twickenham]]: [[1932 Twickenham by-election|1932]] and [[1934 Twickenham by-election|1934]].
*[[Portsmouth South (UK Parliament constituency)|Portsmouth South]]: [[1922 Portsmouth South by-election|1922]] and [[1923 Portsmouth South by-election|1923]].
*[[North Down (UK Parliament constituency)|North Down]]: [[1921 North Down by-election|1921]], [[February 1922 North Down by-election|February]] and [[July 1922 North Down by-election|July 1922]].
*[[West Down (UK Parliament constituency)|West Down]]: [[1921 West Down by-election|1921]] and [[1922 West Down by-election|1922]].
*[[South Londonderry (UK Parliament constituency)|South Londonderry]]: [[1921 South Londonderry by-election|1921]] and [[1922 South Londonderry by-election|1922]].
*[[Louth, Lincolnshire (UK Parliament constituency)|Louth]]: [[1920 Louth by-election|1920]] and [[1921 Louth by-election|1921]].
*[[The Wrekin (UK Parliament constituency)|The Wrekin]]: [[February 1920 The Wrekin by-election|February]] and [[November 1920 The Wrekin by-election|November 1920]].
*[[North Londonderry (UK Parliament constituency)|North Londonderry]]: [[1919 North Londonderry by-election|1919]] and [[1922 North Londonderry by-election|1922]].
*[[Prestwich (UK Parliament constituency)|Prestwich]]: [[January 1918 Prestwich by-election|January]] and [[October 1918 Prestwich by-election|October 1918]].
*[[Edinburgh and St Andrews Universities (UK Parliament constituency)|Edinburgh and St Andrews Universities]]: [[1916 Edinburgh and St Andrews Universities by-election|1916]] and [[1917 Edinburgh and St Andrews Universities by-election|1917]].
*[[St George's Hanover Square (UK Parliament constituency)|St George's Hanover Square]]: [[1913 St George's, Hanover Square by-election|1913]], [[1916 St George's, Hanover Square by-election|1916]] and [[1918 St George's, Hanover Square by-election|1918]].
*[[City of London (UK Parliament constituency)|City of London]]: [[February 1906 City of London by-election|February]] and [[June 1906 City of London by-election|June 1906]].
*[[Oswestry (UK Parliament constituency)|Oswestry]]: [[1901 Oswestry by-election|1901]] and [[1904 Oswestry by-election|1904]].
*[[Southport (UK Parliament constituency)|Southport]]: [[1898 Southport by-election|1898]] and [[1899 Southport by-election|1899]].
*[[City of London (UK Parliament constituency)|City of London]]: [[April 1891 City of London by-election|April]] and [[June 1891 City of London by-election|June 1891]].
*[[Buckingham (UK Parliament constituency)|Buckingham]]: [[1889 Buckingham by-election|1889]] and [[1891 Buckingham by-election|1891]].
*[[Ayr Burghs (UK Parliament constituency)|Ayr Burghs]]: [[1888 Ayr Burghs by-election|1888]] and [[1890 Ayr Burghs by-election|1890]].
*[[Northampton (UK Parliament constituency)|Northampton]]: [[1881 Northampton by-election|1881]], [[1882 Northampton by-election|1882]] and [[1884 Northampton by-election|1884]].
*[[Preston (UK Parliament constituency)|Preston]]: [[1881 Preston by-election|1881]] and [[February 1882 Preston by-election|February]] and [[November 1882 Preston by-election|November 1882]].
*[[Bath (UK Parliament constituency)|Bath]]: [[May 1873 Bath by-election|May]], [[June 1873 Bath by-election|June]] and [[October 1873 Bath by-election|October 1873]].
*[[South Shropshire (UK Parliament constituency)|South Shropshire]]: [[1866 South Shropshire by-election|1866]] and [[1867 South Shropshire by-election|1867]].
*[[East Gloucestershire (UK Parliament constituency)|East Gloucestershire]]: [[January 1854 East Gloucestershire by-election|January]] and [[December 1854 East Gloucestershire by-election|December 1854]].
*[[Greenwich (UK Parliament constituency)|Greenwich]]: [[1851 Greenwich by-election|1851]] and [[1852 Greenwich by-election|1852]].
*[[South Nottinghamshire (UK Parliament constituency)|South Nottinghamshire]]: [[1849 South Nottinghamshire by-election|1848]] and [[1852 South Nottinghamshire by-election|1852]].
*[[Buckinghamshire (UK Parliament constituency)|Buckinghamshire]]: [[1837 Buckinghamshire by-election|1837]] and [[1839 Buckinghamshire by-election|1839]] and [[1842 Buckinghamshire by-election|1842]] and [[1845 Buckinghamshire by-election|1845]], within two successive parliaments.

====Other seats with by-elections less than five years apart====
* [[Batley and Spen (UK Parliament constituency)|Batley and Spen]]: [[2016 Batley and Spen by-election|2016]] and [[2021 Batley and Spen by-election|2021]]
*[[Hemsworth (UK Parliament constituency)|Hemsworth]]: [[1991 Hemsworth by-election|1991]] and [[1996 Hemsworth by-election|1996]].
*[[Upper Bann (UK Parliament constituency)|Upper Bann]]: [[1986 Upper Bann by-election|1986]] and [[1990 Upper Bann by-election|1990]].
*[[Belfast South (UK Parliament constituency)|Belfast South]]: [[1982 Belfast South by-election|1982]] and [[1986 Belfast South by-election|1986]].
*[[Fermanagh and South Tyrone (UK Parliament constituency)|Fermanagh and South Tyrone]]: [[August 1981 Fermanagh and South Tyrone by-election|August 1981]] and [[1986 Fermanagh and South Tyrone by-election|1986]].
*[[Nuneaton (UK Parliament constituency)|Nuneaton]]: [[1965 Nuneaton by-election|1965]] and [[1967 Nuneaton by-election|1967]].
*[[Ormskirk (UK Parliament constituency)|Ormskirk]]: [[1951 Ormskirk by-election|1951]] and [[1953 Ormskirk by-election|1953]].
*[[Liverpool Wavertree (UK Parliament constituency)|Liverpool Wavertree]]: [[1931 Liverpool Wavertree by-election|1931]] and [[1935 Liverpool Wavertree by-election|1935]].
*[[Twickenham (UK Parliament constituency)|Twickenham]]: [[1929 Twickenham by-election|1929]], [[1932 Twickenham by-election|1932]] and [[1934 Twickenham by-election|1934]].
*[[Westminster Abbey (UK Parliament constituency)|Westminster Abbey]]: [[1921 Westminster Abbey by-election|1921]] and [[1924 Westminster Abbey by-election|1924]].

===By-election days===
British Parliamentary elections are invariably held on a Thursday. The last by-election not held on a Thursday was the [[1978 Hamilton by-election]], held on Wednesday 31 May due to a [[FIFA World Cup|World Cup]] opening match on the Thursday evening.

Due to an administrative oversight, the [[1973 Manchester Exchange by-election]] was held on Wednesday 27 June 1973. Prior to that, the last by-elections not held on a Thursday were the [[1965 Saffron Walden by-election]] held on Tuesday 23 March, and the [[1965 Roxburgh, Selkirk and Peebles by-election]] held the following day.

Until the mid-1960s, it was common to hold by-elections on any day of the week (other than Sunday).

===Countermanded poll===
Very occasionally, a scheduled by-election may be overtaken by the calling of a general election and the dissolution of Parliament, in which case the poll is countermanded by the Returning Officer. There have been only three occasions since 1918: a by-election was scheduled to take place in [[Warwick and Leamington (UK Parliament constituency)|Warwick and Leamington]] on 21 November 1923, but was cancelled by a dissolution of Parliament on 16 November. A by-election was scheduled to poll between 13 and 17 October 1924 in [[London University (UK Parliament constituency)|London University]] but was cancelled by a dissolution of Parliament on 9 October. In 2017 the [[2017 Manchester Gorton by-election|Manchester Gorton by-election]] was cancelled by a Motion in the House of Commons following the calling of the [[2017 United Kingdom general election]].<ref>((cite news|title=Manchester Gorton by-election cancellation confirmed|work=BBC News|date=19 April 2017|url=https://www.bbc.co.uk/news/uk-england-manchester-39646993|access-date=20 April 2017))</ref>

===Seats left vacant===
Occasionally seats are left vacant for a substantial period.

No by-election writ was moved for any seat held by [[Sinn Féin]] after the 1918 general election. Four Sinn Féin candidates were elected in two different seats and would have had to decline one of them if they had wanted to take their seats. They were [[Éamon de Valera]] ([[East Clare (UK Parliament constituency)|East Clare]] and [[East Mayo (UK Parliament constituency)|East Mayo]]), [[Arthur Griffith]] ([[East Cavan (UK Parliament constituency)|East Cavan]] and [[North West Tyrone (UK Parliament constituency)|North West Tyrone]]), [[Eoin MacNeill]] ([[Londonderry City (UK Parliament constituency)|Londonderry City]] and [[National University of Ireland (constituency)|National University of Ireland]]) and [[Liam Mellowes]] ([[East Galway (UK Parliament constituency)|East Galway]] and [[North Meath (UK Parliament constituency)|North Meath]]).

By the end of the Parliament, the following Sinn Féin MPs had died without being replaced: [[Pierce McCan]] ([[East Tipperary (UK Parliament constituency)|East Tipperary]]) of [[1918 flu pandemic|influenza]] on 6 March 1919, [[Terence MacSwiney]] ([[Mid Cork (UK Parliament constituency)|Mid Cork]]) following a hunger strike in [[HM Prison Brixton|Brixton prison]] on 25 October 1920, [[Frank Lawless]] ([[North Dublin (UK Parliament constituency)|North Dublin]]) as a result of a riding injury on 16 April 1922, [[Joseph McGuinness]] ([[Longford (UK Parliament constituency)|Longford]]) on 31 May 1922, [[Cathal Brugha]] ([[County Waterford (UK Parliament constituency)|Waterford]]) in action during the [[Irish Civil War]] on 7 July 1922, [[Harry Boland]] ([[South Roscommon (UK Parliament constituency)|South Roscommon]]) shot while being arrested on 2 August 1922, [[Arthur Griffith]] ([[East Cavan (UK Parliament constituency)|East Cavan]] and [[North West Tyrone (UK Parliament constituency)|North West Tyrone]]) on 12 August 1922, and [[Michael Collins (Irish leader)|Michael Collins]] ([[South Cork (UK Parliament constituency)|South Cork]] assassinated on 22 August 1922). In each case their seats were abolished in 1922 as a result of the establishment of the [[Irish Free State]].

Other than these cases the longest time a seat has been left vacant with no by-election held is when [[Dennis Vosper, Baron Runcorn|Dennis Vosper]] was elevated to the Peerage on 20 April 1964, and no writ was moved by the time Parliament was dissolved on 25 September 1964.

==Causes of by-elections==

===By-elections prompted by assassination===

{| class="wikitable"
|-
!Date of assassination  
!Member
!Detail
!By-election
!By-election date
!colspan=2|Defending party
!colspan=2|Winning party
|-
|15 October 2021
|Sir [[David Amess]]
|[[Murder of David Amess|Stabbed during a surgery]] by an Islamic extremist<ref>((Cite news|last=Gibbons|first=Katie|title=Sir David Amess: death threats to British Somalis after MP's murder|language=en|url=https://www.thetimes.co.uk/article/sir-david-amess-death-threats-to-british-somalis-after-mps-murder-320xwbtmn|work=The Times|date=19 October 2021|access-date=4 February 2022|issn=0140-0460))</ref>
|[[2022 Southend West by-election]]
|3 February 2022
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Conservative Party (UK)))
|-
|16 June 2016
|[[Jo Cox]]
|[[Murder of Jo Cox|Cox was killed]] by a white nationalist
|[[2016 Batley and Spen by-election]]
|20 October 2016
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|30 July 1990
|[[Ian Gow]]
|Killed by [[Provisional IRA]] bomb under his car
|[[1990 Eastbourne by-election]]
|18 October 1990
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Democrats (UK)))
|-
|12 October 1984
|Sir [[Anthony Berry]]
|Killed by Provisional IRA bombing of [[Brighton hotel bombing|Brighton]]
|[[1984 Enfield Southgate by-election]]
|13 December 1984
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Conservative Party (UK)))
|-
|14 November 1981
|Rev. [[Robert Bradford (NI politician)|Robert Bradford]]
|Shot by Provisional IRA
|[[1982 Belfast South by-election]]
|4 March 1982
| ((Party name with colour|Ulster Unionist Party))
| ((Party name with colour|Ulster Unionist Party))
|-
|22 June 1922
|Field Marshal Sir [[Sir Henry Wilson, 1st Baronet|Henry Wilson]], Bt.
|Shot outside his home by IRA gunmen
|[[July 1922 North Down by-election]]
|21 July 1922
| ((Party name with colour|Ulster Unionist Party))
| ((Party name with colour|Ulster Unionist Party))
|}

===By-elections prompted by suicide===

{| class="wikitable"
|-
!Member
!By-election
!By-election date
!colspan=2|Defending Party
!colspan=2|Winning Party
|-
|[[Gordon McMaster]]
|[[1997 Paisley South by-election]]
|6 November 1997
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|[[John Heddle]]
|[[1990 Mid Staffordshire by-election]]
|22 March 1990
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|[[Jocelyn Cadbury]]
|[[1982 Birmingham Northfield by-election]]
|28 October 1982
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|[[Bobby Sands]]<sup>1</sup>
|[[August 1981 Fermanagh and South Tyrone by-election|1981 (August) Fermanagh and South Tyrone by-election]]
|20 August 1981
| ((Party name with colour|Anti H-Block))
| ((Party name with colour|Anti H-Block))
|-
|[[Bernard Floud]]
|[[1968 Acton by-election]]
|28 March 1968
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Conservative Party (UK)))
|-
|Sir [[Albert Braithwaite]]
|[[1960 Harrow West by-election]]
|17 March 1960
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Conservative Party (UK)))
|-
|[[Thomas William Stamford|Thomas Stamford]]
|[[1949 Leeds West by-election]]
|21 July 1949
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|[[John Edmondson Whittaker|John Whittaker]]
|[[1946 Heywood and Radcliffe by-election]]
|21 February 1946
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|Sir [[Sir Charles William Cayzer, 3rd Baronet|Charles Cayzer]]<ref>((cite web|url=http://www.leighrayment.com/baronetage/baronetsC2.htm |archive-url=https://web.archive.org/web/20080501224824/http://www.leighrayment.com/baronetage/baronetsC2.htm |archive-date=May 1, 2008 |title=Baronetage |website=Leighrayment.com |url-status=usurped |access-date=1 October 2016))</ref>
|[[1940 City of Chester by-election]]
|7 March 1940
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Conservative Party (UK)))
|-
|[[Anthony Muirhead]]
|[[1939 Wells by-election]]
|13 December 1939
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Conservative Party (UK)))
|-
|[[Edward Marjoribanks (Conservative politician)|Edward Marjoribanks]]
|[[1932 Eastbourne by-election]]
|28 April 1932
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Conservative Party (UK)))
|}

Note
:<sup>1</sup>Death by hunger strike.

===By-elections prompted by accidental death===
{| class="wikitable sortable"
|-
!Date of death  
!Member
!Detail
!By-election
!By-election date
! colspan="2" |Defending party
! colspan="2" |Winning party
|-
|6 September 2014
|[[Jim Dobbin]]
|Died of [[alcohol poisoning]]
|[[2014 Heywood and Middleton by-election]]
|9 October 2014
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|24 February 2000
|[[Michael Colvin]] 
|Killed by a house fire
|[[2000 Romsey by-election]]
|4 May 2000
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Democrats (UK)))
|-
|7 February 1994
|[[Stephen Milligan]]
|Accidentally choked himself while attempting [[autoerotic asphyxia]]
|[[1994 Eastleigh by-election]]
|9 June 1994
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Democrats (UK)))
|-
|12 April 1994
|[[Bob Cryer]]
|Killed in a car crash
|[[1994 Bradford South by-election]]
|9 June 1994
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|22 December 1986
|[[David Penhaligon]]
|Killed in a car crash
|[[1987 Truro by-election]]
|12 March 1987
| ((Party name with colour|Liberal Party (UK)))
| ((Party name with colour|Liberal Party (UK)))
|-
|30 April 1980
|[[Thomas McMillan (British politician)|Thomas McMillan]]
|Died from injuries received in falling from a bus<ref>((Cite news |last=Trotter |first=Stuart |date=1980-05-01 |title=MP Tom McMillan dies in hospital |url=https://news.google.com/newspapers?id=Qvs9AAAAIBAJ&sjid=OkkMAAAAIBAJ&pg=3437,32454 |access-date=2023-06-17 |newspaper=[[The Glasgow Herald]]))</ref>
|[[1980 Glasgow Central by-election]]
|26 June 1980
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|31 October 1962
|[[Jack Jones (Rotherham politician)|Jack Jones]]
|Killed in a car crash
|[[1963 Rotherham by-election]]
|28 March 1963
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|9 December 1958
|[[Sidney Dye]]
|Killed in a car crash
|[[1959 South West Norfolk by-election]]
|25 March 1959
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|3 February 1958
|[[Wilfred Fienburgh]]
|Killed in a car crash
|[[1958 Islington North by-election]]
|15 May 1958
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|3 August 1957
|[[Richard Stokes (politician)|Richard Stokes]]
|Died from injuries received in a car crash
|[[1957 Ipswich by-election]]
|24 October 1957
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|31 January 1953
|Sir [[Walter Smiles]] 
|Killed in the [[MV Princess Victoria]] disaster during the storm surge
|[[1953 North Down by-election]]
|15 April 1953
| ((Party name with colour|Ulster Unionist Party))
| ((Party name with colour|Ulster Unionist Party))
|-
|31 May 1952
|[[Thomas Cook (Scottish politician)|Thomas Cook]]
|Killed in a car crash<ref>((Cite news |date=1952-06-02 |title=Death of Scots Labour MP. Mr Thomas Cook Killed in Road Accident |url=https://news.google.com/newspapers?nid=GGgVawPscysC&dat=19520602&printsec=frontpage&hl=en |access-date=2023-06-17 |newspaper=The Glasgow Herald |page=5))</ref>
|[[1952 Dundee East by-election]]
|17 July 1952
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|3 September 1948
|[[Evan Durbin]] 
|Drowned while swimming
|[[1948 Edmonton by-election]]
|13 November 1948
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|7 October 1947
|[[Joseph Westwood]]
|Killed in a car crash
|[[1948 Stirling and Falkirk by-election]]
|7 October 1948
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|20 December 1947
|Sir [[William Allen (UK politician)|William Allen]]
|Died from injuries received in a road accident
|[[1948 Armagh by-election]]
|5 March 1948
| ((Party name with colour|Ulster Unionist Party))
| ((Party name with colour|Ulster Unionist Party))
|-
|3 June 1947
|Dr [[Richard Clitherow]]
|Died due to an [[Barbiturate overdose|overdose of barbiturates]] after he had been "run down and jaded".<ref name="Clitherow">A verdict of accidental death was recorded at the inquest. Clitherow was a medical doctor and had taken seven barbitone tablets, described by the pathologist as a "bold dose". See ''The Times'', 19 June 1947, p. 2.</ref>
|[[1947 Liverpool Edge Hill by-election]]
|11 September 1947
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|6 February 1947
|[[Ellen Wilkinson]]
|Killed by an accidental overdose of medication
|[[1947 Jarrow by-election]]
|7 May 1947
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|28 December 1945
|[[Francis Beattie (British politician)|Francis Beattie]]
|Killed in a car crash
|[[1946 Glasgow Cathcart by-election]]
|12 February 1946
| ((Party name with colour|Unionist Party (Scotland)))
| ((Party name with colour|Unionist Party (Scotland)))
|-
|27 July 1945
|[[Alfred Dobbs]]
|Killed in a car crash
|[[1945 Smethwick by-election]]
|1 October 1945
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|5 January 1945
|[[James Walker (Labour politician)|James Walker]]
|Killed in a road accident
|[[1945 Motherwell by-election]]
|12 April 1945
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Scottish National Party))
|-
|16 January 1944
|Lieut-Col. [[Frank Heilgers]]
|Killed in the [[1944 Ilford rail crash]]
|[[1944 Bury St Edmunds by-election]]
|29 February 1944
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Conservative Party (UK)))
|-
|9 July 1942
|[[John Jagger (MP)|John Jagger]]
|Killed in a motorcycle accident
|[[1942 Manchester Clayton by-election]]
|17 October 1942
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|-
|15 August 1939
|[[Anthony Crossley]]
|Killed in a plane crash
|[[1939 Stretford by-election]]
|8 December 1939
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Conservative Party (UK)))
|-
|1 May 1933
|[[Antony Bulwer-Lytton, Viscount Knebworth|Viscount Knebworth]]
|Killed in a plane crash
|[[1933 Hitchin by-election]]
|8 June 1933
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Conservative Party (UK)))
|}

===By-elections prompted by posthumous election of MP===
*[[1945 Bromley by-election]]: Sir [[Edward Taswell Campbell]] died before his election declaration at the 1945 general election.
*[[1945 Monmouth by-election]]: [[Leslie Pym]] died before his election declaration at the 1945 general election.
*[[1935 Combined Scottish Universities by-election]]: [[Noel Skelton]] died before his election declaration at the 1935 general election.
*[[1906 North Galway by-election]]: [[Thomas Higgins (Irish politician)|Thomas Higgins]] died before his election declaration at the 1906 general election.

===By-elections prompted by scandal===
*[[2023 Tamworth by-election]]: [[Chris Pincher]] resigned, after losing an appeal against suspension from the House of Commons, in the wake of allegations that he had drunkenly groped two men. The Committee for Standards concluded Pincher's "profoundly damaging" behaviour "represented an abuse of power", causing significant damage to Parliament's reputation. The [[Chris Pincher scandal|scandal]] was also instrumental in the fall of Prime Minister [[Boris Johnson]].
*[[2023 Rutherglen and Hamilton West by-election]]: the seat was declared vacant after [[Margaret Ferrier]] lost a recall petition, after Ferrier was convicted at Glasgow [[Sheriff Court]] of breaching COVID-19 travel rules in 2020, and suspended from the House of Commons.<ref name="Margaret Ferrier">((cite web | url=https://www.bbc.co.uk/news/uk-scotland-scotland-politics-66376464 | title=Margaret Ferrier: Covid breach MP loses seat after recall petition | publisher=BBC | accessdate=1 August 2023 | author=1 August 2023))</ref>
*[[2023 Somerton and Frome by-election]]: [[David Warburton]] resigned in advance of results of investigation into alleged sexual harassment, and his admission to taking cocaine.<ref>((Cite web |last=Mata |first=William |date=2023-06-17 |title=Ex-Tory MP David Warburton resigns after suspension over harassment and drugs claims |url=https://www.independent.co.uk/news/uk/politics/david-warburton-resigns-harassment-by-election-b2359586.html |access-date=2023-06-18 |website=[[The Independent]] |language=en))</ref>
*[[2023 Uxbridge and South Ruislip by-election]]: Former Prime Minister [[Boris Johnson]] resigned 'with immediate effect', in advance of findings of his repeated contempts, and that he deliberately misled Parliament over [[Partygate]], warranting a 90-day suspension.<ref>((Cite news |last=Nevett |first=Joshua |date=2023-06-15 |title=Boris Johnson deliberately misled Parliament over Partygate, MPs find |language=en-GB |work=[[BBC News]] |url=https://www.bbc.com/news/uk-politics-65913692 |access-date=2023-06-18))</ref>
*[[2022 City of Chester by-election]]: [[Chris Matheson (politician)|Chris Matheson]] resigned after being suspended for serious sexual misconduct.<ref>((cite web|url=https://www.bbc.co.uk/news/uk-politics-63344752|title=Labour MP Christian Matheson stands down over sexual misconduct|work=BBC News|date=21 October 2022))</ref>
*[[2022 Tiverton and Honiton by-election]]: [[Neil Parish]] resigned after admitting watching pornography in the House of Commons.
*[[2022 Wakefield by-election]]: [[Imran Ahmad Khan]] resigned after his conviction of sexual assault on a 15-year-old boy.
*[[2021 North Shropshire by-election]]: [[Owen Paterson]] resigned amid controversy surrounding a report by the Parliamentary Commissioner for Standards that found that him [[United Kingdom parliamentary second jobs controversy|broken paid advocacy rules]].
*[[2021 Hartlepool by-election]]: [[Mike Hill (British politician)|Mike Hill]] resigned in advance of an [[employment tribunal]] verdict that he had assaulted, harassed and victimised a parliamentary worker.
*[[2019 Brecon and Radnorshire by-election]]: the seat was declared vacant after [[Chris Davies (Conservative politician)|Chris Davies]] pleaded guilty to filing false expenses claims, and a recall petition was successful.
*[[2019 Peterborough by-election]]: the seat was declared vacant after [[Fiona Onasanya]] was convicted of perverting the course of justice in relation to motoring penalty points issued in 2017. This was the first successful recall petition under the provisions of the [[Recall of MPs Act 2015]].
*[[2018 West Tyrone by-election]]: [[Barry McElduff]] resigned after becoming embroiled in a social media controversy.
*[[2014 Newark by-election]]: [[Patrick Mercer]] resigned after being suspended from the House of Commons for six months by the Parliamentary Standards Committee for asking parliamentary questions in exchange for money.
*[[2013 Eastleigh by-election]]: [[Chris Huhne]] resigned after pleading guilty to perverting the course of justice in relation to persuading his wife to accept motoring penalty points in 2003.
*[[2012 Rotherham by-election]]: [[Denis MacShane]] resigned after [[Standards and Privileges Committee|House of Commons Standards and Privileges Committee]] recommended he be suspended from the service of the House for twelve months; their inquiry arose from the [[United Kingdom Parliamentary expenses scandal]].
*[[2011 Barnsley Central by-election]]: [[Eric Illsley]] resigned after pleading guilty to charges of false accounting arising from the [[United Kingdom Parliamentary expenses scandal]].
*[[2009 Glasgow North East by-election]]: [[Michael Martin, Baron Martin of Springburn|Michael Martin]] resigned as Speaker rather than face a vote of no confidence, amid criticism of his actions arising from the [[United Kingdom Parliamentary expenses scandal]].
*[[2009 Norwich North by-election]]: [[Ian Gibson (politician)|Ian Gibson]] resigned after being debarred as a Labour candidate, due to allegations arising from the [[United Kingdom Parliamentary expenses scandal]].
*[[1997 Beckenham by-election]]: [[Piers Merchant]] resigned after a newspaper story revealed that his previous denials of an affair were lies.
*[[1977 Bournemouth East by-election]]: [[John Cordle]] resigned after he was criticised by a Select Committee for business links to corrupt architect [[John Poulson]].
*[[1976 Walsall North by-election]]: [[John Stonehouse]] resigned after being convicted of insurance fraud.
*[[1973 Berwick-upon-Tweed by-election]]: [[Antony Lambton]] resigned after his visits to prostitutes and use of cannabis were exposed by the ''[[News of the World]]''.
*[[1963 Stratford by-election|1963 Stratford-upon-Avon by-election]]: [[John Profumo]] resigned after his denials of an affair with [[Christine Keeler]] were shown to be lies.
*[[1959 Harrow East by-election]]: [[Ian Harvey (politician)|Ian Harvey]] resigned after conviction for gross indecency with a guardsman in Hyde Park.
*[[1953 Paddington North by-election]]: [[William J. Field|Bill Field]] resigned after conviction for importuning for immoral purposes in a public lavatory.
*[[1949 Sowerby by-election]]: [[John Belcher (politician)|John Belcher]] resigned after being found to have accepted gifts from businessmen for political favours.
*[[1941 Scarborough and Whitby by-election]]: [[Sir Paul Latham, 2nd Baronet|Sir Paul Latham]] resigned after he was arrested to be tried by court-martial on 13 charges of disgraceful conduct.
*[[1936 Derby by-election]]: [[James Henry Thomas]] resigned after being found to have disclosed budget secrets.
*[[1936 Balham and Tooting by-election]]: Sir [[Alfred Butt]] resigned after being found to have disclosed budget secrets.
*[[1931 Pontypridd by-election]]: [[Thomas Isaac Mardy Jones|Thomas Mardy Jones]] resigned after being found to have abused a travel voucher.
*[[1926 Buckrose by-election]]: [[Guy Gaunt]] resigned after being cited as co-respondent in a divorce case.

===By-elections prompted to provide seat for seat-less personality===
*[[1965 Nuneaton by-election]]: For [[Frank Cousins (British politician)|Frank Cousins]].
*[[1965 Leyton by-election]]: For [[Patrick Gordon Walker]] (defeated).
*[[1950 Sheffield Neepsend by-election]]: For [[Frank Soskice]].
*[[February 1940 Southampton by-election]]: For Sir [[John Reith, 1st Baron Reith|John Reith]].
*[[1940 Wandsworth Central by-election]]: For [[Ernest Bevin]].
*[[1922 Portsmouth South by-election]]: For [[Leslie Orme Wilson]].
*[[February 1906 City of London by-election]]: For [[Arthur Balfour]].
*[[1896 Montrose Burghs by-election]]: For [[John Morley, 1st Viscount Morley of Blackburn|John Morley]].

===By-elections prompted by party disputes and defections===
By-elections are ostensibly to vote for a 'person', not a 'party', meaning that a member switching parties mid-term is not cause for a by-election. However, some members do seek re-election under their new party as a point of principle.
{| class="wikitable sortable"
|-
!Member of Parliament
!By-election
!colspan=2|Former party
!colspan=2|New party
!Details
|-
|[[Stephen Phillips (British politician)|Stephen Phillips]]
|[[2016 Sleaford and North Hykeham by-election]]
| ((Party name with colour|Conservative Party (UK)))
| || Did not contest
|Resigned, citing irreconcilable differences with his party owing to a "lurch to the right", he could no longer accept the appellation "Conservative" or continue to represent his constituents.
|-
|[[Mark Reckless]]
|[[2014 Rochester and Strood by-election]]
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|UKIP))
|Joined the UK Independence Party over policy on European Union membership referendum.
|-
|[[Douglas Carswell]]
|[[2014 Clacton by-election]]
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|UKIP))
|Joined the UK Independence Party over policy on European Union membership referendum.
|-
|[[Bob Mellish, Baron Mellish|Robert Mellish]]
|[[1983 Bermondsey by-election]]
| ((Party name with colour|Labour Party (UK)))
| || Did not contest
|Disenchanted with left-wing takeover of his [[Constituency Labour Party]] (CLP), obtained a job with the [[London Docklands Development Corporation]], left the Labour Party and resigned to force a by-election.
|-
|[[Bruce Douglas-Mann]]
|[[1982 Mitcham and Morden by-election]]
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Social Democratic Party (UK)))
|Sought re-election having defected to newly formed SDP; defeated by Conservative candidate.
|-
|[[Dick Taverne, Baron Taverne|Dick Taverne]]
|[[1973 Lincoln by-election]]
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Democratic Labour Party (UK, 1972)))
|Sought re-election as an Independent 'Democratic Labour' candidate after being deselected by his CLP; he was successful.
|-
|[[Ray Gunter]]
|[[1972 Southwark by-election]]
| ((Party name with colour|Labour Party (UK)))
| || Did not contest
|Resigned from the Labour Party in disagreement with its stance opposing [[European Economic Community]] entry.
|-
|[[Victor Raikes]]
|[[1957 Liverpool Garston by-election]]
| ((Party name with colour|Conservative Party (UK)))
| || Did not contest
|Resigned the Conservative whip over the Suez crisis, and then resigned from Parliament on obtaining a business appointment in [[Southern Rhodesia]].
|-
|[[Stanley Evans]]
|[[1957 Wednesbury by-election]]
| ((Party name with colour|Labour Party (UK)))
| || Did not contest
|Supported the Conservative government's Suez policy, resigned after being asked to by his Constituency Labour Party.
|-
|[[Anthony Nutting]]
|[[1956 Melton by-election]]
| ((Party name with colour|Conservative Party (UK)))
| || Did not contest
|Minister of State for Foreign Affairs, resigned in protest at Suez invasion policy. 
|-
|[[William Allen Jowitt]] 
|[[1929 Preston by-election]]
| ((Party name with colour|Liberal Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|Sought re-election as Labour Party candidate having been offered role of Attorney General by Ramsay MacDonald.
|-
|[[Joseph Kenworthy]]
|[[1926 Kingston upon Hull Central by-election]]
| ((Party name with colour|Liberal Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|Sought re-election as Labour Party candidate following disillusion with leadership of Lloyd George.
|-
|[[J. E. B. Seely, 1st Baron Mottistone|J. E. B. Seely]]
|[[1904 Isle of Wight by-election]]
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Independent politician))
|Resigned seat in opposition to Conservative policy. Returned unopposed as an independent Conservative and subsequently re-elected in 1906 as a Liberal MP. 
|-
|[[Cathcart Wason]]
|[[1902 Orkney and Shetland by-election]]
| ((Party name with colour|Liberal Party (UK)))
| ((Party name with colour|Independent politician))
|Resigned and successfully re-contested his seat
|}

===By-elections resulting from Members resigning on principle===
*[[2024 Kingswood by-election]]: [[Chris Skidmore]] resigned in opposition to a bill that allows the issuance of new oil and gas licences.
*[[2016 Richmond Park by-election]]: [[Zac Goldsmith]] resigned to force a by-election on the issue of [[Expansion of Heathrow Airport|the expansion of Heathrow Airport]], and contested as an Independent. He was defeated by [[Sarah Olney]] of the Liberal Democrats. Goldsmith later regained his seat the following year at the [[2017 United Kingdom general election|2017 general election]].
*[[2008 Haltemprice and Howden by-election]]: [[David Davis (British politician)|David Davis]] resigned to force a by-election on the issue of civil liberties. He was re-elected with neither of the other main parties contesting the seat.
*[[1986 Northern Ireland by-elections]]: Fifteen Unionist MPs resigned and re-contested their seats in protest at the [[Anglo-Irish Agreement]]. All but one was re-elected.
*[[1963 Bristol South East by-election]]: [[Malcolm St Clair (politician)|Malcolm St Clair]] honoured a pledge to stand down if law changed to allow [[Tony Benn]] to disclaim his peerage.
*[[1938 Kinross and Western Perthshire by-election|1938 Kinross-shire and Perthshire by-election]]: The [[Katharine Marjory Stewart-Murray, Duchess of Atholl|Duchess of Atholl]] resigned in protest at [[Neville Chamberlain]]'s appeasement policy and sought re-election. She was defeated.
*[[1927 Southwark North by-election]]: [[Leslie Haden-Guest]] resigned from the Labour Party over its policy on China, and re-contested the seat as an Independent [[Constitutionalist]] with Conservative support. He was defeated, finishing bottom of the poll. The Liberals gained the seat.
*[[1927 Leith by-election]]: [[William Wedgwood Benn, 1st Viscount Stansgate|William Wedgwood Benn]] resigned following his resignation from the Liberal party and joining the Labour Party. He did not contest the by-election out of fairness to the existing Labour candidate. The seat was narrowly held by a new Liberal candidate.
*[[1914 Cork City by-election]]: [[William O'Brien]] resigned to submit himself to the voters after the [[Irish Parliamentary Party|Irish Nationalists]] had made council gains in Cork. He was returned unopposed.
*[[1912 Bow and Bromley by-election]]: [[George Lansbury]] resigned to contest his seat on the issue of [[Women's Suffrage]], although he was disenchanted with a range of Labour party policies. He was defeated.
*[[1909 Stratford-on-Avon by-election]]: [[Thomas Kincaid-Smith]] resigned from the Liberal Party on the issue of compulsory national service. He stood as an Independent with [[National Service League]] support. He was defeated, finishing bottom of the poll.
*[[1906 Mid Cork by-election]]: [[D. D. Sheehan]] resigned and re-contested his seat following his expulsion from the Irish Nationalist group for not signing the party pledge. Re-elected as an independent.

===By-elections prompted by Member's desire to contest another seat===
*[[1918 East Tyrone by-election]]: [[William Redmond (1886–1932)|William Redmond]] resigned in order to defend his late father's seat at [[Waterford City (UK Parliament constituency)|Waterford City]]. He was successful.
*[[1914 East Worcestershire by-election]]: [[Austen Chamberlain]] resigned in order to defend his late father's seat at [[Birmingham West (UK Parliament constituency)|Birmingham West]]. He was successful.
*[[1911 East Wicklow by-election]]: [[John Muldoon (politician)|John Muldoon]] resigned in order to contest the [[East Cork (UK Parliament constituency)|East Cork by-election]]. He was successful.

===By-elections caused by the previous result being declared void===
((main|List of UK Parliamentary election petitions))

*[[2011 Oldham East and Saddleworth by-election]]: The result of the [[2010 United Kingdom general election|2010 general election]] was declared void because the victor was found guilty of knowingly making false statements about a rival candidate.
*[[1997 Winchester by-election]]: The result of the [[1997 United Kingdom general election|1997 general election]] was declared void because ballot papers which had not received the official mark would have affected the result, if counted. Liberal Democrat [[Mark Oaten]] massively increased the minute majority he had achieved in the [[1997 United Kingdom general election|general election]].
*[[1924 Oxford by-election]]: The result of the [[1923 United Kingdom general election|1923 general election]] was declared void because there were irregularities in the election expenses of the successful candidate.
*[[1923 Berwick-upon-Tweed by-election]]: The result of the [[1922 United Kingdom general election|1922 general election]] was declared void because there were irregularities in the election expenses of the successful candidate.
*[[1911 North Louth by-election]]: The result of the [[December 1910 United Kingdom general election|December 1910 general election]] was declared void because of corrupt practices and bribery on the part of the successful candidate.

===By-elections prompted by disqualification of the sitting Member===
*[[1961 Bristol South East by-election]]: [[Tony Benn]] had inherited a [[Peerage of the United Kingdom|Peerage]] from his father. Although by-elections were routinely called where Members had succeeded to the Peerage, the seat was not considered vacated until the Member had received a [[Hereditary peer#Writs of summons|Writ of Summons]] to the [[House of Lords]], and Benn, who refused to accept the Peerage, did not apply for one. The seat was declared vacant by a resolution of the House of Commons.
*[[1956 Mid Ulster by-election]]: [[Charles Beattie]] was found to be disqualified through membership of National Assistance panels. A bill indemnifying him from the consequences of acting as an MP while disqualified was passed by the House of Commons; Beattie did not stand in the by-election. 
*[[1955 Mid Ulster by-election]]: [[Tom Mitchell (Irish politician)|Tom Mitchell]] was disqualified as a felon (resolution of the House).
*[[1950 Belfast West by-election]]: Rev [[James Godfrey MacManaway]] was found by the [[Judicial Committee of the Privy Council]] to be disqualified, as a Minister of the [[Church of Ireland]].
*[[1925 Walsall by-election]]: [[William Preston (UK politician)|William Preston]] was found to be disqualified owing to his holding government contracts. A bill indemnifying him was passed by the House of Commons and Preston was re-elected at the by-election.
*[[1924 Dover by-election]]: [[John Astor, 1st Baron Astor of Hever|John Astor]] was disqualified for voting before he took the oath. He was returned unopposed at the by-election.
*[[1913 Whitechapel by-election]]: Sir [[Stuart Samuel]] was found to be disqualified owing to his holding government contracts. A bill indemnifying him was passed by the House of Commons and Samuel was narrowly re-elected at the by-election.
*[[1904 City of London by-election]]: [[Alban Gibbs, 2nd Baron Aldenham|Alban Gibbs]] was found to be disqualified owing to his holding government contracts. Gibbs resigned and was re-elected unopposed at the by-election.
*[[1904 St Albans by-election]]: [[Vicary Gibbs (St Albans MP)|Vicary Gibbs]] was found to be disqualified owing to his holding government contracts. Gibbs resigned and was narrowly defeated at the by-election.

===By-elections prompted by expulsion from the House===
*[[1955 South Norfolk by-election]]: [[Peter Baker (UK politician)|Peter Baker]] was expelled after being convicted of [[uttering]] forged documents.
*[[1947 Gravesend by-election]]: [[Garry Allighan]] was expelled after being found to be in extreme contempt of the House by his peers after selling details of private parliamentary meetings to the ''[[Evening Standard]]''.
*[[1922 Hackney South by-election]]: [[Horatio Bottomley]] was expelled after being convicted of fraud, perjury and false accounting.
*[[1903 Galway Borough by-election]]: the seat was declared vacant after [[Arthur Lynch (politician)|Arthur Alfred Lynch]] was convicted of high treason after fighting on the Boer side in the [[Second Boer War]].

===By-elections prompted by lunacy===
*[[1916 Colne Valley by-election]]: [[Charles Leach]] was adjudged a lunatic and his seat declared vacant.

===By-elections prompted by bankruptcy===
*[[1928 Ashton-under-Lyne by-election]]: [[Cornelius Homan]] lost his seat after being declared bankrupt.
*[[1922 Camberwell North by-election]]: [[Henry Newton Knights]] lost his seat after being declared bankrupt.
*[[1914 North Galway by-election]]: [[Richard Hazleton]] resigned before being declared bankrupt. He discharged his bankruptcy and was returned in the by-election.
*[[1912 Hackney South by-election]]: [[Horatio Bottomley]] resigned after filing a bankruptcy petition. 
*[[1909 South Kilkenny by-election]]: [[Nicholas Joseph Murphy]] was declared bankrupt.

===By-elections prompted for miscellaneous reasons===
*[[1916 Widnes by-election]]: [[William Walker, 1st Baron Wavertree|William Hall Walker]] resigned to permit him to donate his thoroughbred racing stock to create a National Stud in an "arms-length" transaction. He was returned unopposed at the by-election.

===By-elections prompted by death of member on wartime active service===

====Second World War====
*[[1945 Chelmsford by-election]]: [[John Macnamara]] was killed in action fighting in Italy.
*[[1944 Berwick-upon-Tweed by-election]]: [[George Charles Grey]] was killed in action fighting in Normandy, France.
*[[1944 Bury St Edmunds by-election]]: [[Frank Heilgers]] was killed in a train crash in Ilford.
*[[1943 Acton by-election]]: [[Hubert Duggan]] died of tuberculosis contracted on active service. <sup>a</sup>
*[[1943 Darwen by-election]]: [[Stuart Russell (politician)|Stuart Russell]] died of fever on active service in Egypt. 
*[[1943 Chippenham by-election]]: [[Victor Cazalet]] was killed in a plane crash in Gibraltar while escorting General Sikorski. 
*[[1943 Birmingham Aston by-election]]: [[Edward Orlando Kellett]] was killed in action fighting in North Africa. 
*[[1943 Buckingham by-election]]: [[John Whiteley (politician)|John Whiteley]] was killed in a plane crash in Gibraltar while escorting General Sikorski.
*[[1943 Bristol Central by-election]]: [[Allen Bathurst, Lord Apsley|Lord Apsley]] was killed in action in a plane crash in the Middle-East. 
*[[1943 King's Lynn by-election]]: [[Somerset Arthur Maxwell|Somerset Maxwell]] died of wounds received at the Battle of El Alamein. 
*[[1942 Salisbury by-election]]: [[James Despencer-Robertson]] died suddenly, apparently from overwork as military secretary at Southern Command Headquarters. <sup>b</sup>
*[[1942 Llandaff and Barry by-election]]: [[Patrick Munro]] died while taking part in an exercise for the Home Guard at Westminster. 
*[[1941 The Wrekin by-election]]: [[James Baldwin-Webb]] drowned when the SS [[City of Benares]] was torpedoed.
*[[1941 Dudley by-election]]: [[Dudley Joel]] was killed in action while serving with the Royal Navy. 
*[[1941 Bodmin by-election]]: [[John Rathbone (Bodmin)|John Rathbone]] was killed in action on bombing operations over Germany. 
*[[1941 Hitchin by-election]]: Sir [[Arnold Wilson]] was killed in action over northern France while a gunner in Bomber Command
*[[1941 King's Norton by-election]]: [[Ronald Cartland]] was killed in action during the retreat to Dunkirk. 
*[[1940 Manchester Exchange by-election]]: [[Peter Eckersley (cricketer)|Peter Eckersley]] was killed in action in a plane crash while serving with the Fleet Air Arm.
*[[1940 Heywood and Radcliffe by-election]]: [[Richard Whitaker Porritt|Richard Porritt]] was killed in action fighting in Belgium.
*[[1939 Wells by-election]]: [[Anthony Muirhead]] committed suicide owing to his fear that a leg-injury might prevent his service in the War. <sup>b</sup>

:Notes: The above list is of those members either mentioned as having died on War Service in a written Commons answer from Prime Minister [[Winston Churchill]] on 19 January 1945, or who appear in the ''House of Commons Book of Remembrance'' unveiled in 1949.

:<sup>a</sup> Mentioned in the written Commons answer, but does not appear in the ''House of Commons Book of Remembrance''.
:<sup>b</sup> Not mentioned in the written Commons answer, but does appear in the ''House of Commons Book of Remembrance''.

:NB: The above list does not include the names of three members whose deaths on active service were overtaken by the 1945 general election. For a complete list see [[Records of members of parliament of the United Kingdom#Second World War]]

====First World War====
*[[October 1918 Prestwich by-election]]: [[Oswald Cawley]] had been killed in action in France.
*[[1918 Bath by-election]]: [[Lord Alexander Thynne]] had been killed in action in France.
*[[1918 Canterbury by-election]]: [[Francis Bennett-Goldney]] had been killed by an on-duty car accident in France.
*[[1918 Ross by-election]]: [[Percy Clive]] had been killed in action in France.
*[[1918 Manchester South by-election]]: [[Philip Glazebrook]] had been killed in action in Palestine.
*[[1917 Wisbech by-election]]: The Hon [[Neil Primrose (politician)|Neil Primrose]] died of wounds received in Palestine.
*[[1917 Spalding by-election]]: The Hon [[Francis McLaren]] had been killed in a flying accident serving with the [[Royal Flying Corps]].
*[[1917 East Clare by-election]]: [[Willie Redmond]] had been killed in action in Belgium.
*[[1917 Henley by-election]]: [[Valentine Fleming]] had been killed by shell fire in France.
*[[1916 North Ayrshire by-election]]: [[Duncan Frederick Campbell]] had died in England of wounds received from a landmine on the Western Front.
*[[1916 Winchester by-election]]: The Hon [[Guy Baring]] had been killed in the [[Battle of the Somme]] in France.
*[[1916 Tewkesbury by-election]]: [[Michael Hicks Beach, Viscount Quenington]] had died of wounds in Egypt.
*[[1915 St Austell by-election]]: The Hon [[Thomas Agar-Robartes]] had died of wounds received in the [[Battle of Loos]] in France.
*[[1915 Cardiff by-election]]: [[Lord Ninian Crichton-Stuart]] had been killed in action in France.
*[[1915 Uxbridge by-election]]: The Hon [[Charles Thomas Mills]] had been killed in action in France.
*[[1915 Heywood by-election]]: [[Harold Thomas Cawley]] had been killed in action in the [[Battle of Gallipoli]].
*[[1915 Kilmarnock Burghs by-election]]: [[William Glynne Charles Gladstone]] had been killed in action in France.
*[[1915 Mid Antrim by-election]]: The Hon [[Arthur O'Neill]] had been killed in action in the [[Ypres Salient]] in Belgium.

((Incomplete list|date=August 2008))

==Miscellaneous records==

===Incumbents fall directly from first place to third place===

*[[1995 Littleborough and Saddleworth by-election]] Conservative loss, gained by the Liberal Democrats
*[[1995 Perth and Kinross by-election]] Conservative loss, gained by the SNP
*[[1994 Eastleigh by-election]] Conservative loss, gained by the Liberal Democrats
*[[1985 Brecon and Radnor by-election]] Conservative loss, gained by the Liberals
*[[1982 Mitcham and Morden by-election]]<sup>1</sup> Labour loss, gained by the Conservatives
*[[1958 Rochdale by-election]] Conservative loss, gained by Labour
*[[1934 Merthyr by-election]] ILP loss, gained by Labour
*[[1929 Holland with Boston by-election]] Conservative loss, gained by the Liberals
*[[1927 Bosworth by-election]] Conservative loss, gained by the Liberals
*[[1926 Kingston upon Hull Central by-election]]<sup>2</sup> Liberal loss, gained by Labour
*[[1920 South Norfolk by-election]] Liberal loss, gained by Labour

:<sup>1</sup> [[Bruce Douglas-Mann]] had been re-elected as Labour MP for the seat in the 1979 general election. In 1981, along with several other MPs, he defected to the newly formed [[Social Democratic Party (UK)|Social Democratic Party]]. Against his new colleagues' advice, he honoured a pledge to face his electors under his new party colours and precipitated a by-election. He came second in the by-election which was won by the Conservatives. The new Labour candidate finished third.

:<sup>2</sup> the Liberal MP, Lt-Commander the Hon. [[Joseph Kenworthy, 10th Baron Strabolgi|Joseph Montague Kenworthy]], defected to Labour and sought re-election under his new colours. He was successful, and the new Liberal candidate lost his deposit.

===Incumbent government gains seats===
These records show the rare occasions when the government won a seat they had not won at the previous general election.

{| class="wikitable"
!colspan=2|Party
!By-election
!colspan=2|Losing party
|-
| ((Party name with colour|rowspan=11|Conservative Party (UK)))
|[[2021 Hartlepool by-election]]
| ((Party name with colour|rowspan=6|Labour Party (UK)))
|-
|[[2017 Copeland by-election]]
|-
|[[1982 Mitcham and Morden by-election]]
|-
|[[1961 Bristol South-East by-election]]<sup>1</sup>
|-
|[[1960 Brighouse and Spenborough by-election]]
|-
|[[1953 Sunderland South by-election]]
|-
|[[1926 Combined English Universities by-election]]
| ((Party name with colour|Liberal Party (UK)))
|-
|[[1923 Berwick-upon-Tweed by-election]]<sup>3</sup>
| ((Party name with colour|National Liberal Party (UK, 1922)))
|-
|[[1922 Hackney South by-election]]<sup>b</sup>
| ((Party name with colour|Independent politician))
|-
|[[1921 Woolwich East by-election]]<sup>b</sup>
| ((Party name with colour|Labour Party (UK)))
|-
|[[1920 Stockport by-election]]<sup>2b</sup>
| ((Party name with colour|Coalition Labour))
|-
| ((Party name with colour|rowspan=3|Labour Party (UK)))<sup>a</sup>
|[[1929 Liverpool Scotland by-election]]<sup>4</sup>
| ((Party name with colour|Nationalist Party (Ireland)))
|-
|[[1929 Preston by-election]]<sup>5</sup>
| ((Party name with colour|Liberal Party (UK)))
|-
|[[1924 Liverpool West Toxteth by-election]]
| ((Party name with colour|Conservative Party (UK)))
|-
| ((Party name with colour|rowspan=4|Liberal Party (UK)))
|[[1913 Chesterfield by-election]]
| ((Party name with colour|Labour Party (UK)))
|-
|[[1913 Londonderry City by-election]]
| ((Party name with colour|Irish Unionist Alliance))
|-
|[[1912 Hanley by-election]]
| ((Party name with colour|Labour Party (UK)))
|-
|[[1912 Hackney South by-election]]
| ((Party name with colour|Independent politician))
|}

====Notes====
:<sup>1</sup> Seat awarded by Election Court to Conservative runner-up because Labour victor deemed ineligible.
:<sup>2</sup> An arguable gain; Stockport was a two-member seat; in the 1918 general election it was won by two supporters of the Coalition Government, one a Liberal and one a Labour member. After a death and a resignation, a by-election was held for both seats. The seats were again won by two Coalition Government supporters, but this time a Conservative and a Liberal, while a Labour candidate who did not support the government was unsuccessful.
:<sup>3</sup> National Liberal elected in 1922 election had his election declared void (electoral fraud). Resulting by-election was a gain for the Conservatives.
:<sup>4</sup> Uncontested gain from [[Irish Nationalist]].
:<sup>5</sup> Liberal MP defected to Labour and was re-elected as Labour at a by-election the Liberals did not contest.
:<sup>a</sup>Labour won both the [[2000 West Bromwich West by-election]] and [[2009 Glasgow North East by-election]], regarded as a gain from the contest at the United Kingdom general elections in 1997 and 2005 respectively as those seats had been contested by the then Speakers of the House of Commons. Prior to assuming the Speakership they had both been elected as Labour MPs.
:<sup>b</sup>The Conservatives were in Coalition government, led by the Liberal Prime Minister, [[David Lloyd George]].

===Principal Opposition loses seats===

These records show the rare occasions when the official Opposition failed to hold on to a seat they had won at the previous General election.

{|class="wikitable"
|-
!colspan=2|Lost by
!colspan=2|Gained by
!By-election
|-
| ((Party name with colour|rowspan=5|Conservative Party (UK)))
| ((Party name with colour|Liberal Democrats  (UK)))
|[[2000 Romsey by-election]]
|-
| ((Party name with colour|Unity (Northern Ireland)))
|[[1969 Mid Ulster by-election]] (from Ulster Unionist)
|-
| ((Party name with colour|Liberal Party (UK)))
|[[1965 Roxburgh, Selkirk and Peebles by-election]]
|-
| ((Party name with colour|Empire Free Trade Crusade))
|[[1930 Paddington South by-election]]<sup>1</sup>
|-
| ((Party name with colour|Labour Party (UK)))
|[[1924 Liverpool West Toxteth by-election]]
|-
| ((Party name with colour|rowspan=16|Labour Party (UK)))
| ((Party name with colour|rowspan=2|Conservative Party (UK)))
|[[2021 Hartlepool by-election]]
|-
|[[2017 Copeland by-election]]
|-
| ((Party name with colour|Respect Party))
|[[2012 Bradford West by-election]]
|-
| ((Party name with colour|Scottish National Party))
|[[1988 Glasgow Govan by-election]]
|-
| ((Party name with colour|Social Democratic Party (UK)))
|[[1987 Greenwich by-election]]
|-
| ((Party name with colour|Liberal Party (UK)))
|[[1983 Bermondsey by-election]]
|-
| ((Party name with colour|Conservative Party (UK)))
|[[1982 Mitcham and Morden by-election]]
|-
| ((Party name with colour|Scottish National Party))
|[[1973 Glasgow Govan by-election]]
|-
| ((Party name with colour|Democratic Labour Party (UK, 1972)))
|[[1973 Lincoln by-election]]
|-
| ((Party name with colour|Liberal Party (UK)))
|[[1972 Rochdale by-election]]
|-
| ((Party name with colour|Conservative Party (UK)))
|[[1961 Bristol South East by-election]]<sup>2</sup>
|-
| ((Party name with colour|Conservative Party (UK)))
|[[1960 Brighouse and Spenborough by-election]]
|-
| ((Party name with colour|Conservative Party (UK)))
|[[1953 Sunderland South by-election]]
|-
| ((Party name with colour|Liberal Party (UK)))
|[[1927 Southwark North by-election]]
|-
| ((Party name with colour|Liberal Party (UK)))
|[[1923 Anglesey by-election]]<sup>3</sup>
|-
| ((Party name with colour|Unionist Party (UK)))
|[[1921 Woolwich East by-election]]<sup>4</sup>
|}

:<sup>1</sup>A confused situation, where the victorious [[Empire Free Trade Crusade]] candidate was effectively a right-wing unofficial Conservative, who subsequently took the whip and was re-elected as official Conservative candidate.
:<sup>2</sup>seat awarded by Election Court to Conservative runner-up because Labour victor [[Tony Benn|Viscount Stansgate]] was deemed ineligible.
:<sup>3</sup>Sir [[Owen Thomas (politician)|Owen Thomas]] had been elected as Independent Labour, took the whip for a while, before reverting to Independent Labour.
:<sup>4</sup>Lost to Coalition Conservatives (see [[Coalition Coupon]])

===By-election holds overturned at next general election===

On rare occasions a party has failed to overturn an incumbent in the by-election yet has gone on to gain the seat at the subsequent general election.

{| class="wikitable sortable"
|-
!! scope="col" | By-election
!! scope="col" colspan=2| Held by
!! scope="col" colspan=2| Gain by
!! scope="col" | General election
|-
|[[2019 Peterborough by-election]]
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Conservative Party (UK)))
|[[2019 United Kingdom general election|2019]]
|-
|[[2013 Eastleigh by-election]]
| ((Party name with colour|Liberal Democrats (UK)))
| ((Party name with colour|Conservative Party (UK)))
|[[2015 United Kingdom general election|2015]]
|-
|[[2011 Inverclyde by-election]]
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Scottish National Party))
|[[2015 United Kingdom general election|2015]]
|-
|[[2006 Blaenau Gwent by-election]]
| ((Party name with colour|Independent politician))
| ((Party name with colour|Labour Party (UK)))
|[[2010 United Kingdom general election|2010]]
|-
|[[1986 South Down by-election]]
| ((Party name with colour|Ulster Unionist Party))
| ((Party name with colour|Social Democratic and Labour Party))
|[[1987 United Kingdom general election|1987]]
|-
|[[1983 Darlington by-election]]
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Conservative Party (UK)))
|[[1983 United Kingdom general election|1983]]
|-
|[[1973 Dundee East by-election]]
| ((Party name with colour|Labour Party (UK)))
| ((Party name with colour|Scottish National Party))
|[[February 1974 United Kingdom general election|February 1974]]
|-
|[[1960 Bolton East by-election]]
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|[[1964 United Kingdom general election|1964]]
|-
|[[1928 Carmarthen by-election]]
| ((Party name with colour|Liberal Party (UK)))
| ((Party name with colour|Labour Party (UK)))
|[[1929 United Kingdom general election|1929]]
|-
|[[1905 New Forest by-election]]
| ((Party name with colour|Conservative Party (UK)))
| ((Party name with colour|Liberal Party (UK)))
|[[1906 United Kingdom general election|1906]]
|}

===By-election victors had not contested previous general election===
It is unusual for a political party which has not contested a seat at a general election to take it at a subsequent by-election. Independent candidates are not included.

{| class="wikitable"
|-
!By-election
!!scope="col" colspan=2| Gain by
!Majority percentage
|-
|[[2014 Rochester and Strood by-election]]
| ((Party name with colour|UK Independence Party))<sup>4</sup>
|7.3
|-
|[[2014 Clacton by-election]]
| ((Party name with colour|UK Independence Party))<sup>4</sup>
|35.1
|-
|[[2000 South Antrim by-election]]
| ((Party name with colour|Democratic Unionist Party))
|2.7
|-
|[[1995 North Down by-election]]
| ((Party name with colour|UK Unionist Party))
|10.6
|-
|[[1982 Glasgow Hillhead by-election]]
| ((Party name with colour|Social Democratic Party (UK)))<sup>1</sup>
|6.8
|-
|[[1981 Crosby by-election]]
| ((Party name with colour|Social Democratic Party (UK)))<sup>1</sup>
|9.2
|-
|[[April 1981 Fermanagh and South Tyrone by-election]]
| ((Party name with colour|Anti H-Block))
|2.4
|-
|[[1973 Isle of Ely by-election]]
| ((Party name with colour|Liberal Party (UK)))
|3.3
|-
|[[1973 Lincoln by-election]]
| ((Party name with colour|Democratic Labour Party (UK, 1972)))<sup>2</sup>
|35.0
|-
|[[1969 Mid Ulster by-election]]
| ((Party name with colour|Unity (Northern Ireland)))
|6.6
|-
|[[1967 Hamilton by-election]]
| ((Party name with colour|Scottish National Party))
|4.5
|-
|[[1958 Torrington by-election]]
| ((Party name with colour|Liberal Party (UK)))
|0.6
|-
|[[1945 Chelmsford by-election]]
| ((Party name with colour|Common Wealth Party))
|15.0
|-
|[[1945 Motherwell by-election]]
| ((Party name with colour|Scottish National Party))
|2.8
|-
|[[1944 Skipton by-election]]
| ((Party name with colour|Common Wealth Party))
|12.4
|-
|[[1943 Eddisbury by-election]]
| ((Party name with colour|Common Wealth Party))
|2.7
|-
|[[1943 Belfast West by-election]]
| ((Party name with colour|Northern Ireland Labour Party))
|12.8
|-
|[[1936 Ross and Cromarty by-election]]
| ((Party name with colour|National Labour Organisation))
|16.5
|-
|[[1936 Combined Scottish Universities by-election]]
| ((Party name with colour|National Labour Organisation))
|25.3
|-
|[[1934 Merthyr by-election]]
| ((Party name with colour|Labour Party (UK)))
|23.0
|-
|[[1930 Paddington South by-election]]
| ((Party name with colour|Empire Free Trade Crusade))
|4.7
|-
|[[1929 Liverpool Scotland by-election]]
| ((Party name with colour|Labour Party (UK)))
|''unopposed''
|-
|[[1926 Kingston upon Hull Central by-election]]
| ((Party name with colour|Labour Party (UK)))
|15.3
|-
|[[1923 Mitcham by-election]]
| ((Party name with colour|Labour Party (UK)))
|3.9
|-
|[[1921 Kirkcaldy Burghs by-election]]
| ((Party name with colour|Labour Party (UK)))
|6.8
|-
|[[1921 Woolwich East by-election]]
| ((Party name with colour|Unionist Party (UK)))<sup>3</sup>
|2.6
|}

Notes:

:<sup>1</sup> Alliance partner the Liberal party had contested the seat.
:<sup>2</sup> The victor was the sitting MP, who had left the Labour party.
:<sup>3</sup> Candidate endorsed by the coalition government.
:<sup>4</sup> The victor was the sitting MP, who had left the Conservative party.

===Additional victories by minor parties===
In addition to the above section, other minor party successes include the following. For a complete list, see the [[list of UK minor party and independent MPs elected]].
{| class="wikitable"
!Candidate
!colspan=2|Party
!By-election
!Votes
!Percentage
|-
|[[George Galloway]]
| ((Party name with colour|Respect Party))
|[[2012 Bradford West by-election]]
|18,341
|52.8
|-
|[[Dai Davies (politician)|Dai Davies]]
| ((Party name with colour|Independent politician))
|[[2006 Blaenau Gwent by-election]]
|12,543
|46.7
|-
|[[James Kilfedder]]
| ((Party name with colour|Ulster Popular Unionist Party))
|[[1986 North Down by-election]]
|30,793
|79.2
|-
|[[Owen Carron]]
| ((Party name with colour|Anti H-Block))
|[[August 1981 Fermanagh and South Tyrone by-election|1981 (August) Fermanagh and South Tyrone by-election]]
|31,278
|49.1
|-
|[[George Forrest (Northern Ireland politician)|George Forrest]]
| ((Party name with colour|Independent Unionist))
|[[1956 Mid Ulster by-election]]
|28,605
|48.4
|-
|[[James Carmichael (British politician)|James Carmichael]]
| ((Party name with colour|Independent Labour Party))
|[[1946 Glasgow Bridgeton by-election]]
|6,351
|34.3
|}

====Minor parties other strong performance====
Parties without representation in the House of Commons which saved their [[deposit (politics)|deposit]]:

{| class="wikitable sortable"
!
!Party
!By-election
!Candidate
!Votes
!Percentage
!Position
!Notes
|-
| ((Party name with colour|Alliance Party of Northern Ireland))
|[[1986 Belfast East by-election]]
|[[Oliver Napier]]
|5,917
|17.4
|2
|Party historically represented at Westminster
|-
| ((Party name with colour|Alliance Party of Northern Ireland))
|[[1986 Belfast North by-election]]
|[[Paul Maguire (judge)|Paul Maguire]]
|5,072
|16.7
|2
|Party historically represented at Westminster
|-
| ((Party name with colour|Alliance Party of Northern Ireland))
|[[1982 Belfast South by-election]]
|[[David Cook (Northern Ireland politician)|David Cook]]
|11,726
|26.9
|2
|Party historically represented at Westminster
|-
| ((Party name with colour|Alliance Party of Northern Ireland))
|[[1986 Belfast South by-election]]
|[[David Cook (Northern Ireland politician)|David Cook]]
|7,635
|25.0
|2
|Party historically represented at Westminster
|-
| ((Party name with colour|Alliance Party of Northern Ireland))
|[[1986 East Antrim by-election]]
|[[Seán Neeson]]
|5,405
|15.1
|2
|Party historically represented at Westminster
|-
| ((Party name with colour|Alliance Party of Northern Ireland))
|[[1986 North Down by-election]]
|[[John Cushnahan]]
|8,066
|20.8
|2
|Party historically represented at Westminster
|-
| ((Party name with colour|Alliance Party of Northern Ireland))
|[[1995 North Down by-election]]
|[[Oliver Napier]]
|6,970
|25.4
|3
|Party historically represented at Westminster
|-
| ((Party name with colour|Alliance Party of Northern Ireland))
|[[2000 South Antrim by-election]]
|[[David Ford (politician)|David Ford]]
|2,031
|6.6
|5
|Party represented in the Northern Ireland Assembly and historically at Westminster
|-
| ((Party name with colour|All Party Alliance))
|[[1968 Oldham West by-election]]
|[[John Creasey]]
|3,389
|13.2
|3
|
|-
| ((Party name with colour|Brexit Party))
|[[2019 Peterborough by-election]]
|Mike Greene
|9,801 
|28.9
|2
|Party represented in the European Parliament
|-
| ((Party name with colour|Brexit Party))
|[[2019 Brecon and Radnorshire by-election]]
|Des Parkinson
|3,331
|10.5
|3
|Party represented in the European Parliament
|-
| ((Party name with colour|British National Party))
|[[1994 Dagenham by-election]]
|[[John Tyndall (politician)|John Tyndall]]
|1,511
|7.0
|4
|
|-
| ((Party name with colour|British National Party))
|[[2011 Barnsley Central by-election]]
|Enis Dalton
|1,463
|6.0
|4
|Party represented in the European Parliament
|-
| ((Party name with colour|British National Party))
|[[2007 Sedgefield by-election]]
|Andrew Spence
|2,494
|8.9
|4
|
|-
| ((Party name with colour|British National Party))
|[[2012 Rotherham by-election]]
|Marlene Guest
|1,804
|8.5
|3
|Party represented in the European Parliament
|-
| ((Party name with colour|English Democrats Party))
|[[2008 Haltemprice and Howden by-election]]
|Joanne Robinson
|1,714
|7.2
|3
|
|-
| ((Party name with colour|Green Party of England and Wales))
|[[2008 Haltemprice and Howden by-election]]
|Shan Oakes
|1,758
|7.4
|2
|Party represented in the European Parliament and subsequently at Westminster
|-
| ((Party name with colour|Green Party of England and Wales))
|[[2009 Norwich North by-election]]
|[[Rupert Read]]
|3,350
|9.7
|5
|Party represented in the European Parliament and subsequently at Westminster
|-
| ((Party name with colour|Green Party (UK)))
|[[1989 Vauxhall by-election]]
|Henry Bewley
|1,767
|6.1
|4
|Party represented in the House of Lords
|-
| ((Party name with colour|Independent politician))
|[[2013 Mid Ulster by-election]]
|Nigel Lutton
|12,781
|34.4
|2
|[[Democratic Unionist Party|DUP]], [[Ulster Unionist Party|UUP]] and [[Traditional Unionist Voice|TUV]] did not stand candidates and supported Lutton's candidacy<ref>((cite web |title=Mid Ulster TUV Chair Signs Lutton's Nomination Papers |url=http://www.tuv.org.uk/press-releases/view/1765/mid-ulster-tuv-chair-signs-lutton's-nomination-papers|archive-url=https://archive.today/20130424002726/http://www.tuv.org.uk/press-releases/view/1765/mid-ulster-tuv-chair-signs-lutton's-nomination-papers |date=18 February 2013 |archive-date=24 April 2013))</ref><ref>((cite web|last=Purdy |first=Martina |url=https://www.bbc.com/news/uk-northern-ireland-21462044 |title=Mid Ulster by-election: Lutton chosen as unionist candidate |publisher=BBC News |date=14 February 2013 |access-date=1 October 2016))</ref>
|-
| ((Party name with colour|Independent politician))
|[[1946 Combined English Universities by-election]]
|[[Mary Stocks]]
|5,124
|28.0
|2
|
|-
| ((Party name with colour|Independent politician))
|[[1946 Combined English Universities by-election]]
|[[Ernest Simon, 1st Baron Simon of Wythenshawe|Ernest Simon]]
|4,028
|22.0
|3
|
|-
| ((Party name with colour|Independent politician))
|[[2021 Hartlepool by-election]]
|Sam Lee
|2,904
|9.7
|3
|
|-
| ((Party name with colour|Independent politician))
|[[2022 Wakefield by-election]]
|Akef Akbar
|2,090
|7.7
|3
|
|-
| ((Party name with colour|Independent politician))
|[[1986 East Londonderry by-election]]
|Peter Barry
|2,001
|6.1
|2
|Fictitious paper candidate running as "For the Anglo-Irish Agreement"
|-
| ((Party name with colour|Independent politician))
|[[2013 South Shields by-election]]
|Ahmed Khan
|1,331
|5.4
|4
|
|-
| ((Party name with colour|Independent politician))
|[[2011 Barnsley Central by-election]]
|Tony Devoy
|1,266
|5.2
|5
|
|-
| ((Party name with colour|Independent politician))
|[[1999 Hamilton South by-election]]
|Stephen Mungall
|1,075
|5.5
|5
|
|-
| ((Party name with colour|Independent politician))
|[[2007 Sedgefield by-election]]
|Paul Gittins
|1,885
|6.7
|5
|
|-
| ((Party name with colour|Independent politician))
|[[1986 South Antrim by-election]]
|Peter Barry
|1,870
|5.9
|2
|Fictitious paper candidate running as "For the Anglo-Irish Agreement"
|-
| ((Party name with colour|Independent politician))
|[[1986 Strangford by-election]]
|Peter Barry
|1,993
|5.8
|2
|Fictitious paper candidate running as "For the Anglo-Irish Agreement"
|-
| ((Party name with colour|Independent Labour))
|[[1946 Combined English Universities by-election]]
|S. Wormald
|3,414
|18.7
|4
|
|-
| ((Party name with colour|Independent Labour))
|[[1991 Liverpool Walton by-election]]
|[[Lesley Mahmood]]
|2,613
|6.5
|3
|
|-
| ((Party name with colour|Independent Unionist))
|[[1946 Down by-election]]
|J. Hastings-Little
|16,895
|17.1
|3
|
|-
| ((Party name with colour|Independent Unionist))
|[[1995 North Down by-election]]
|Alan Chambers
|2,170
|7.9
|4
|
|-
| ((Party name with colour|Irish Anti-Partition League))
|[[1948 Armagh by-election]]
|[[James O'Reilly (Irish politician)|James O'Reilly]]
|16,284
|40.3
|2
|
|-
| ((Party name with colour|Irish Labour Party))
|[[1950 Belfast West by-election]]
|[[Jack Beattie]]
|30,833
|49.2
|2
|Party previously and later represented at Westminster
|-
| ((Party name with colour|Lincolnshire Independents))
|[[2016 Sleaford and North Hykeham by-election]]
|Marianne Overton
|2,892
|8.8
|5
|
|-
|
|[[National Fellowship]]
|[[1963 Bristol South East by-election]]
|[[Edward Martell (politician)|Edward Martell]]
|4,834
|19.0
|2
|
|-
| ((Party name with colour|National Front (United Kingdom)))
|[[1973 West Bromwich by-election]]
|[[Martin Webster]]
|4,789
|16.0
|3
|
|-
| ((Party name with colour|Northern Ireland Labour Party))
|[[1959 Belfast East by-election]]
|James Gardner
|14,264
|42.2
|2
|Party represented in the Parliament of Northern Ireland and previously at Westminster
|-
| ((Party name with colour|Northern Ireland Labour Party))
|[[1952 Belfast South by-election]]
|[[Samuel Napier (Northern Irish politician)|Samuel Napier]]
|7,655
|24.9
|2
|Party previously represented at Westminster
|-
| ((Party name with colour|Northern Ireland Labour Party))
|[[1963 Belfast South by-election]]
|Norman Searight
|7,209
|25.8
|2
|Party represented in the Parliament of Northern Ireland and previously at Westminster
|-
| ((Party name with colour|Northern Ireland Labour Party))
|[[1946 Down by-election]]
|[[Desmond Donnelly]]
|28,846
|29.3
|2
|Party represented in the Parliament of Northern Ireland and previously at Westminster
|-
| ((Party name with colour|Peace Party (UK)))
|[[2012 Middlesbrough by-election]]
|Imdad Hussain
|1,060
|6.3
|5
|
|-
| ((Party name with colour|Plaid Cymru))
|[[1946 Aberdare by-election]]
|[[Wynne Samuel]]
|7,090
|20.0
|2
|Party later represented at Westminster
|-
| ((Party name with colour|Plaid Cymru))
|[[1954 Aberdare by-election]]
|[[Gwynfor Evans]]
|5,671
|16.0
|2
|Party later represented at Westminster
|-
| ((Party name with colour|Plaid Cymru))
|[[1972 Merthyr Tydfil by-election]]
|[[Emrys Roberts (Plaid Cymru politician)|Emrys Roberts]]
|11,852
|37.0
|2
|Party previously and later represented at Westminster
|-
| ((Party name with colour|Plaid Cymru))
|[[1946 Ogmore by-election]]
|T. R. Morgan
|5,685
|29.4
|2
|Party later represented at Westminster
|-
| ((Party name with colour|People Before Profit Alliance))
|[[2011 Belfast West by-election]]
|[[Gerry Carroll]]
|1,751
|7.6
|3
|Two members elected to the Dáil in 2011
|-
| ((Party name with colour|Reform UK))
|[[2021 Old Bexley and Sidcup by-election]]
|[[Richard Tice]]
|1,432
|6.6
|3
|
|-
| ((Party name with colour|Reform UK))
|[[2023 Tamworth by-election]]
|Ian Cooper
|1,373
|5.4
|3
|
|-
| ((Party name with colour|RESPECT The Unity Coalition))
|[[2004 Birmingham Hodge Hill by-election]]
|[[John Rees (activist)|John Rees]]
|1,282
|6.3
|4
|[[George Galloway]] MP was a party member, but was usually considered Independent Labour in Parliament at the time
|-
| ((Party name with colour|RESPECT The Unity Coalition))
|[[2004 Leicester South by-election]]
|[[Yvonne Ridley]]
|3,724
|12.7
|4
|[[George Galloway]] MP was a party member, but was usually considered Independent Labour in Parliament at the time
|-
| ((Party name with colour|Social Democratic and Labour Party))
|[[2018 West Tyrone by-election]]
|[[Daniel McCrossan]]
|6,254
|17.9
|3
|Party represented in the Northern Ireland Assembly and historically at Westminster 
|-
| ((Party name with colour|Scottish National Party))
|[[1946 Glasgow Bridgeton by-election]]
|M. Wood
|2,575
|13.9
|4
|Party previously and later represented at Westminster
|-
| ((Party name with colour|Scottish National Party))
|[[1961 Glasgow Bridgeton by-election]]
|Ian MacDonald
|3,549
|18.7
|3
|Party previously and later represented at Westminster
|-
| ((Party name with colour|Scottish National Party))
|[[1967 Glasgow Pollok by-election]]
|[[George Leslie (politician)|George Leslie]]
|10,884
|29.2
|3
|Party previously and later represented at Westminster
|-
| ((Party name with colour|Scottish National Party))
|[[1970 South Ayrshire by-election]]
|Sam Purdie
|7,785
|19.9
|3
|Party previously and later represented at Westminster
|-
| ((Party name with colour|Scottish National Party))
|[[1962 West Lothian by-election]]
|[[William Wolfe]]
|9,750
|23.3
|2
|Party previously and later represented at Westminster
|-
| ((Party name with colour|Scottish Socialist Party))
|[[2000 Falkirk West by-election]]
|Iain Hunter
|989
|5.1
|4
|Party represented in the Scottish Parliament
|-
| ((Party name with colour|Scottish Socialist Party))
|[[2000 Glasgow Anniesland by-election]]
|Charlie McCarthy
|1,441
|7.2
|5
|Party represented in the Scottish Parliament
|-
| ((Party name with colour|Scottish Socialist Party))
|[[1999 Hamilton South by-election]]
|Shareen Blackall
|1,847
|9.5
|3
|Party represented in the Scottish Parliament
|-
| ((Party name with colour|Social Democratic Party (UK, 1990)))
|[[1991 Neath by-election]]
|John Warman
|1,826
|5.3
|5
|Party of same name which was dissolved in 1990 was represented in Parliament
|-
| ((Party name with colour|Socialist Alliance (England)))
|[[2000 Preston by-election]]
|Terry Cartwright
|1,210
|5.7
|4
|
|-
| ((Party name with colour|Socialist Alliance (England)))
|[[2000 Tottenham by-election]]
|Weyman Bennett
|885
|5.4
|4
|
|-
| ((Party name with colour|Socialist Labour Party (UK)))
|[[1996 Barnsley East by-election]]
|Ken Capstick
|949
|5.3
|4
|
|-
| ((Party name with colour|Socialist Labour Party (UK)))
|[[1996 Hemsworth by-election]]
|Brenda Nixon
|1,193
|5.4
|4
|
|-
| ((Party name with colour|Socialist Labour Party (UK)))
|[[2002 Ogmore by-election]]
|Christopher Herriot
|1,152
|6.3
|5
|
|-
| ((Party name with colour|UK Independence Party))
|[[2004 Hartlepool by-election]]
|Stephen Allison
|2,347
|10.2
|3
|Party represented in the European Parliament
|-
| ((Party name with colour|UK Independence Party))
|[[2006 Bromley and Chislehurst by-election]]
|[[Nigel Farage]]
|2,347
|8.1
|3
|Party represented in the European Parliament
|-
| ((Party name with colour|UK Independence Party))
|[[2009 Norwich North by-election]]
|Glenn Tingle
|4,068
|11.8
|4
|Party represented in the European Parliament
|-
| ((Party name with colour|UK Independence Party))
|[[2011 Oldham East and Saddleworth by-election]]
|[[Paul Nuttall]]
|2,029
|5.8
|4
|Party represented in the European Parliament
|-
| ((Party name with colour|UK Independence Party))
|[[2011 Barnsley Central by-election]]
|[[Jane Collins]]
|2,953
|12.2
|2
|Party represented in the European Parliament
|-
| ((Party name with colour|UK Independence Party))
|[[2011 Feltham and Heston by-election]]
|Andrew Charalambous
|1,276
|5.5
|4
|Party represented in the European Parliament
|-
| ((Party name with colour|UK Independence Party))
|[[2012 Cardiff South and Penarth by-election]]
|Simon Zeigler
|1,179
|6.1
|5
|Party represented in the European Parliament
|-
| ((Party name with colour|UK Independence Party))
|[[2012 Corby by-election]]
|Margot Parker
|5,108
|14.3
|3
|Party represented in the European Parliament
|-
| ((Party name with colour|UK Independence Party))
|[[2012 Rotherham by-election]]
|[[Jane Collins]]
|4,648
|21.8
|2
|Party represented in the European Parliament
|-
| ((Party name with colour|UK Independence Party))
|[[2012 Middlesbrough by-election]]
|Richard Elvin
|1,990
|11.8
|2
|Party represented in the European Parliament
|-
| ((Party name with colour|UK Independence Party))
|[[2012 Croydon North by-election]]
|[[Winston McKenzie]]
|1,400
|5.7
|3
|Party represented in the European Parliament
|-
| ((Party name with colour|UK Independence Party))
|[[2013 Eastleigh by-election]]
|[[Diane James]]
|11,571
|27.8
|2
|Party represented in the European Parliament
|-
| ((Party name with colour|UK Independence Party))
|[[2013 South Shields by-election]]
|Richard Elvin
|5,988
|24.2
|2
|Party represented in the European Parliament
|-
| ((Party name with colour|UK Independence Party))
|[[2014 Wythenshawe and Sale East by-election]]
|John Bickley
|4,301
|18.0
|2
|Party represented in the European Parliament
|-
| ((Party name with colour|UK Independence Party))
|[[2014 Newark by-election]]
|[[Roger Helmer]]
|10,028
|25.9
|2
|Party represented in the European Parliament
|-
| ((Party name with colour|UK Independence Party))
|[[2014 Heywood and Middleton by-election]]
|John Bickley
|11,016
|38.7
|2
|Party represented in the European Parliament, and also represented in the House of Commons following the [[2014 Clacton by-election|Clacton by-election]] the same day.
|-
| ((Party name with colour|Ulster Unionist Party))
|[[2018 West Tyrone by-election]]
|Chris Smyth
|2,909
|8.3
|4
|Party represented in the Northern Ireland Assembly and historically at Westminster 
|-
| ((Party name with colour|Workers' Party (Ireland)))
|[[1986 Belfast North by-election]]
|[[Seamus Lynch]]
|3,563
|11.8
|3
|
|-
| ((Party name with colour|Workers' Party (Ireland)))
|[[1986 Lagan Valley by-election]]
|[[John Lowry (Irish politician)|John Lowry]]
|3,328
|9.3
|2
|
|-
| ((Party name with colour|Workers' Party (Ireland)))
|[[1986 Upper Bann by-election]]
|[[Tom French (politician)|Tom French]]
|6,978
|19.2
|2
|
|-
| ((Party name with colour|Workers Party of Britain))
|[[2021 Batley and Spen by-election]]
|[[George Galloway]]
|8,264
|21.9
|3
|
|}

===Victory from third or lower place===

* [[2022 Tiverton and Honiton by-election]], gained by the Liberal Democrats
* [[2021 North Shropshire by-election]], gained by the Liberal Democrats. 
* [[2012 Bradford West by-election]], gained by Respect, from fifth place
* [[2004 Leicester South by-election]], gained by the Liberal Democrats
* [[2003 Brent East by-election]], gained by the Liberal Democrats
* [[1988 Glasgow Govan by-election]], gained by the SNP, from fourth place
* [[1987 Greenwich by-election]], gained by the SDP
* [[1985 Brecon and Radnor by-election]], gained by the Liberals
* [[1983 Bermondsey by-election]], gained by the Liberals
* [[1981 Croydon North West by-election]], gained by the Liberals
* [[1973 Glasgow Govan by-election]], gained by the SNP
* [[1973 Berwick-upon-Tweed by-election]], gained by the Liberals
* [[1973 Ripon by-election]], gained by the Liberals
* [[1972 Sutton and Cheam by-election]], gained by the Liberal
* [[1966 Carmarthen by-election]], gained by Plaid Cymru
* [[1962 Orpington by-election]], gained by the Liberals
* [[1929 Holland with Boston by-election]], gained by the Liberals

===Incumbent party did not contest===

*[[2016 Richmond Park by-election]] (incumbent Conservative MP ran as an Independent with party backing)
*[[1995 North Down by-election]] ([[Ulster Popular Unionist Party]] disintegrated before by-election)
*[[1963 Bristol South East by-election]] (Conservative candidate awarded seat after 1961 by-election had agreed to stand aside, if law changed to permit disqualified Labour candidate to take his seat)
*[[1942 Cardiff East by-election]] (Conservatives stood aside to allow election of National Government minister)
*[[1940 City of London by-election]] (Conservatives stood aside to allow election of National Government minister)
*[[February 1940 Southampton by-election]] (National Liberals stood aside to allow election of National Government minister)
*[[1938 Combined Scottish Universities by-election]] (National Labour stood aside to allow election of National Government minister)
*[[1936 Ross and Cromarty by-election]] (National Liberals stood aside to allow election of National Government minister from National Labour)
*[[1936 Combined Scottish Universities by-election]] (Conservatives stood aside to allow election of National Government minister from National Labour)
*[[1935 Perth by-election]] (Conservatives stood aside to allow election of National Liberal)
*[[1929 Liverpool Scotland by-election]] (lone mainland Irish Nationalist was essentially a Labour supporter)
*[[1929 Preston by-election]] (Liberals acquiesced to [[William Jowitt]] becoming Labour's [[Attorney General]])

===Losers had been unopposed at previous election===
*[[1930 Paddington South by-election]] Conservative loss, gained by Empire Free Trade Crusade.
*[[1929 Liverpool Scotland by-election]] Irish Nationalist loss, gained by Labour.<sup>1</sup>
*[[1928 Halifax by-election]] Speaker loss, gained by Labour.<sup>2</sup>
*[[1921 Kirkcaldy Burghs by-election]] Coalition Liberal loss, gained by Labour.
*[[1921 Woolwich East by-election]] Labour loss, gained by Conservative.
*[[February 1920 The Wrekin by-election]] Coalition Liberal loss, gained by Independent.

Notes:
:<sup>1</sup> the Nationalists did not contest the by-election
:<sup>2</sup> the Speaker had originally been a Liberal MP.

===Major party did not run===

====Great Britain====
Labour joined the Liberal Democrats and the Greens in not contesting the [[2022 Southend West by-election]], out of respect following [[murder of David Amess|the murder]] of the previous MP, Sir [[David Amess]].

The Conservatives declined to run a candidate in the [[2016 Richmond Park by-election]], instead backing Conservative incumbent [[Zac Goldsmith]], who was designated as an Independent.

The Conservatives, Liberal Democrats, UKIP, and Green Party declined to run candidates in the [[2016 Batley and Spen by-election]], due to the circumstances regarding [[Killing of Jo Cox|the killing]] of the previous MP, [[Jo Cox]].

Neither the Liberal Democrat nor the Labour Party stood candidates in the [[2008 Haltemprice and Howden by-election]]. The by-election was a single-issue election in regards to government security policy, in which the Liberal Democrats supported the Conservative candidate.

The Conservative Party did not run a candidate in the [[1963 Bristol South East by-election]], the [[1957 Carmarthen by-election]], the [[1948 Paisley by-election]] or the [[1946 Ogmore by-election]].

The Labour Party did not run in the [[1945 City of London by-election]], the [[1945 Kensington South by-election]] or the [[1946 Combined English Universities by-election]].

Prior to 2008, the last by-election without an official Liberal Democrat, Liberal or SDP candidate had been the [[1994 Newham North East by-election]]; the Lib Dems nominated a candidate, but he joined the Labour Party before the election. No official Liberal candidate was nominated for the [[1980 Glasgow Central by-election]], whilst no Liberal stood in either the [[1973 Westhoughton by-election]] or the [[1973 West Bromwich by-election]], both held on 24 May 1973.

The last Scottish by-elections without official [[Scottish National Party]] candidates were the [[1965 Roxburgh, Selkirk and Peebles by-election]] and the [[1964 Rutherglen by-election]].

Plaid Cymru did not stand a candidate for the [[2019 Brecon and Radnorshire by-election]], choosing instead to endorse the Liberal Democrat candidate in a "Stop Brexit" alliance. Prior to that, the last Welsh by-elections without official Welsh Nationalist candidates were the [[1950 Abertillery by-election]], the [[1946 Pontypool by-election]] and the [[1945 Monmouth by-election]].

====Northern Ireland====
The more fluid nature of politics in Northern Ireland makes it harder to define all major parties. In addition many by-elections have not been contested by parties holding other seats in the House of Commons, whether due to agreements with other parties, poor organisation in the constituency or the particular circumstances on the by-election. However, for the period since 1981 (which saw the first by-elections in twelve years, during which time several major political realignments had occurred) the main parties are usually considered to be the [[Democratic Unionist Party]], [[Sinn Féin]], the [[Social Democratic and Labour Party]] (SDLP) and the [[Ulster Unionist Party]].

At the [[2013 Mid Ulster by-election]]. a single "unity" candidate was backed by the withdrawal of the Democratic Unionist Party, Ulster Conservatives and Unionists and Traditional Unionist Voice. Prior to Mid Ulster in 2013, the most recent examples of by-elections without official Democratic Unionist candidates were the [[1995 North Down by-election]] and the [[1990 Upper Bann by-election]]. They also did not stand in the twelve seats held by other Unionist parties in the [[1986 Northern Ireland by-elections|15 by-elections in 1986]].

The last by-election without official candidates from either Sinn Féin or the SDLP was the [[1995 North Down by-election]]. Both parties also declined to stand in the eleven Unionist majority seats in the [[1986 Northern Ireland by-elections|15 by-elections in 1986]]. The SDLP also did not contest either the [[April 1981 Fermanagh and South Tyrone by-election|April]] or [[August 1981 Fermanagh and South Tyrone by-election|August]] 1981 by-elections in [[Fermanagh and South Tyrone (UK Parliament constituency)|Fermanagh and South Tyrone]].

The last by-elections without official Ulster Unionist candidates prior to Mid Ulster in 2013 were North Antrim, East Belfast, Mid Ulster and North Down in the [[1986 Northern Ireland by-elections|15 by-elections in 1986]].

The main British parties have generally not stood in seats in Northern Ireland. The by-election exceptions are the [[1990 Upper Bann by-election]] (NI Conservatives and [[Social Democratic Party (UK, 1988)|continuing SDP]]) and the [[1995 North Down by-election]] (NI Conservatives). Prior to the 1970s the Ulster Unionists were effectively the local Conservatives, whilst the [[Ulster Liberal Party|Liberals]] contested some but not all seats. The SDLP has traditionally seen itself as a "sister party" to the British Labour party, and its MPs usually accept the Labour whip in Parliament.

=== Miscellaneous notable results ===
It is unusual for one of the major parties to finish outside of the top three in England and Wales (or outside of the top four in Scotland). It is also unusual for the principal opposition party to suffer a significant reverse in its share of the vote or ranking.

*The [[2021 Hartlepool by-election]], with a 16% [[Swing (United Kingdom)|swing]] to the Conservatives, was the Labour Party's worst result in a Labour-held seat while the party was in Opposition, since the [[1912 Hanley by-election]]. It was effectively the party's worst-ever result since it became a major party.
*The [[2019 Brecon and Radnorshire by-election]] saw Labour finish fourth behind the Liberal Democrats, Conservatives and Brexit Party. In addition, UKIP fell to last place, behind the Official Monster Raving Loony Party – a result compared to the continuing SDP's defeat in the 1990 Bootle by-election.<ref>((cite news|title=Brecon and Radnorshire by-election result: Ukip beaten by Monster Raving Loony party|url=https://www.independent.co.uk/news/uk/politics/brecon-radnorshire-by-election-result-ukip-monster-raving-loony-party-lady-wales-lady-lily-pink-a9036411.html|first=Adam|last=Forrest|date=2 August 2019|access-date=5 August 2019|newspaper=The Independent))</ref><ref>((cite news|url=https://www.theneweuropean.co.uk/top-stories/monster-raving-loony-party-finishes-off-ukip-by-beating-them-in-by-election-1-6195062|title=Monster Raving Loony Party 'finishes off' UKIP by beating them in by-election|first=Jonathon|last=Read|date=2 August 2019|access-date=5 August 2019|newspaper=The New European|archive-date=5 August 2019|archive-url=https://web.archive.org/web/20190805101914/https://www.theneweuropean.co.uk/top-stories/monster-raving-loony-party-finishes-off-ukip-by-beating-them-in-by-election-1-6195062|url-status=dead))</ref>
*The [[2016 Richmond Park by-election]] was the first Liberal Democrat gain since 2010, showing tentative signs of recovery for the party. It also gave them a female MP for the first time in the 56th parliament. In addition it was the first occasion in more than a century of Labour losing their deposit in a London by-election.
*The [[2014 Clacton by-election]] saw the election of the first UKIP MP on the largest swing ever against the Conservative Party. It was also the first time that a party had gained a seat not having contested the previous election since the [[1973 Isle of Ely by-election]]. The Liberal Democrat's 1.4% of the vote was their worst result in an English seat since 1924.
*The [[2013 Eastleigh by-election]] delivered several records. It was the first time in an English seat that both Labour and Conservative finished outside of the top two. For the first time, UKIP came close to winning a seat. It was the closest three-cornered English by-election since the [[1921 Penistone by-election]], and, aside from the [[1946 Combined English Universities by-election]], it was won with the lowest winning share of the vote since 1918. Aside from the contrived example of the [[1989 Richmond (Yorks) by-election]] it was also the first time Labour had finished fourth in a by-election while in Opposition.
*At the [[2012 Rotherham by-election]], the Conservative party fell from second to fifth place (equalling its previous lowest position in a by-election in mainland Britain) while the Liberal Democrats fell from third place to eighth, the lowest ranking ever achieved by a major party in a by-election. This followed the [[2011 Barnsley Central by-election]], where the Liberal Democrats took sixth place, dropping from second at the [[2010 United Kingdom general election|2010 general election]]. The Rotherham by-election was also the first recorded by-election result to have women in the top four places.
*In the [[2009 Glasgow North East by-election]] and [[1999 Hamilton South by-election]] the Liberal Democrats came sixth in both cases, equalling the worst ever placing by a major party in the UK. In 1999 the party had 634 votes while in Glasgow the party won 474 votes.
*At the [[2008 Henley by-election]] the Labour Party finished in fifth place, the worst ranking for the party in its history, and a record low for any government in a UK mainland constituency. The lowest ever for an incumbent government was the [[1990 Upper Bann by-election]] when the Conservatives came sixth, although they had not previously contested the seat.
*At the [[2006 Blaenau Gwent by-election]], held on the same day as Bromley and Chislehurst, the Conservative Party's fifth-place ranking equalled the worst-place achieved by a major party in England or Wales, a feat the Conservatives had first achieved in the same seat in the 2005 general election. The Blaenau victor, [[Dai Davies (politician)|Dai Davies]] was the first independent to hold a seat previously occupied by an independent since [[Charles Vere Ferrers Townshend|Sir C.V.F. Townshend]] held [[The Wrekin (UK Parliament constituency)|The Wrekin]] in 1920.
*The drop in the Conservative share of the vote, 11.1%, at the [[2006 Bromley and Chislehurst by-election]] was their worst result in a Conservative-held seat while in opposition since 1930<sup>1</sup>. At the same by-election, the Labour Party's fall from second to fourth place was the first time the party had suffered such a reverse in an English seat.
*The Conservative Party fell from second to fourth place in the [[2004 Hartlepool by-election]]  and the [[1983 Bermondsey by-election]], and fell from third to fourth place in the [[1991 Liverpool Walton by-election]]. At the time their worst ranking in an English by-election since at least 1945 was the drop from third place to fourth place in the [[1974 Newham South by-election]].
*The Labour party fell from second to fourth place in the [[2000 Ceredigion by-election]].
*At the [[Bootle (UK Parliament constituency)|Bootle by-election, 1990]] the "continuing" [[Social Democratic Party (UK, 1988)|SDP]] finished seventh out of eight candidates, behind the [[Monster Raving Loony Party]], in a seat parts of which had once been in adjoining [[Crosby (UK Parliament constituency)|Crosby]], scene of the party's greatest triumph only eight years previously.
*The Labour Party achieved fourth place in the [[1989 Richmond (Yorks) by-election]] although this was contrived somewhat by the [[Liberal Democrats (UK)|Social and Liberal Democrats]] and [[Social Democratic Party (UK, 1988)|Social Democratic Party]] parties running separate candidates.
*At the [[1976 Walsall North by-election]], the Liberal Party could take only fifth place. Beaten by an independent and a minor party candidate, at the time, this was the worst placing for any major party in an English by-election since at least 1945.
*The last time the Liberals lost a by-election they were defending was at the [[1957 Carmarthen by-election]], defeated by the former Liberal MP turned Labour candidate, Lady [[Megan Lloyd George]]. The Liberal parliamentary contingent was thus reduced to five MPs, its lowest ever level.

Notes
<sup>1</sup>Excluding the [[1931 Westminster St George's by-election]] and the [[1930 Paddington South by-election]], which were essentially intra-Conservative contests, the previous worst result was, ironically, the [[1930 Bromley by-election]]

==By-elections having national significance==
*[[2022 Tiverton and Honiton by-election]] and [[2022 Wakefield by-election]]: A pair of by-election losses for the government on the same day – one in a rural area represented by the Conservatives since 1923 and one in a recently won "[[Red wall (British politics)|Red Wall]]" seat – triggered the resignation of [[Oliver Dowden]] as [[Chairman of the Conservative Party]] and contributed to the pressure on Prime Minister Boris Johnson that led to [[July 2022 United Kingdom government crisis|the collapse of his government]] two weeks later.
*[[2017 Copeland by-election]]: A Conservative win in a previously safe Labour seat confirmed the party's [[Opinion polling for the United Kingdom general election, 2017|strong opinion poll lead]] and prompted an [[2017 United Kingdom general election|early election]].
*[[2016 Richmond Park by-election]]: After losing most of its seats in the 2015 general election, a Lib Dem gain on a large swing in a strongly [[2016 United Kingdom European Union membership referendum|Remain]] seat marked the beginning of a turnaround for the party and demonstrated the political effects of [[Brexit]].
*[[2014 Clacton by-election]]: The first by-election victory for the [[UK Independence Party]]
*[[2008 Crewe and Nantwich by-election]]: A Conservative gain (from Labour in this case) at a by-election for the first time since 1982, and the first time as an opposition party since 1978, demonstrated the Conservatives were back in contention to possibly win the next general election.
*[[2003 Brent East by-election]]: A Lib Dem gain of a Labour safe seat on a 29% swing demonstrated the political effect of public dissatisfaction with the [[Iraq War]]. 
*[[1997 Wirral South by-election]]: A Labour gain on a large swing just weeks before a general election confirmed the move in the party's favour was real and meant the Conservatives became a [[minority government]].
*[[1991 Liverpool Walton by-election]]: The [[Militant tendency|Militant]] group, as Walton Real Labour, opposed a Labour candidate for the first time; their showing led to the decision to re-organise as Militant Labour without using [[Entryism|entryist]] tactics.
*[[May 1990 Bootle by-election]]: Abysmal showing of the '[[Social Democratic Party (UK, 1988)|continuing SDP]]' led to the party being wound up.
*[[1987 Greenwich by-election]]: Defeat of a left-wing Labour candidate demonstrated the party's vulnerability.
*[[1983 Darlington by-election]]: Labour's successful defence of a marginal seat stabilised the party, and secured the position of Leader [[Michael Foot]].
*[[1981 Crosby by-election]]: Victory of the [[Social Democratic Party (UK)|Social Democratic Party]] in a rock-solid Conservative seat showed the national appeal of the party.
*[[April 1981 Fermanagh and South Tyrone by-election]]: Election of Maze prison hunger-striker [[Bobby Sands]] demonstrated that nationalist voters could support violent Republican candidates; taken by the Republican movement as a vindication of their stance, it led to the return of Sinn Féin as a major force in Northern Irish politics.
*[[1977 Birmingham Stechford by-election]]: The loss of the seat to the Conservatives tipped Labour under [[James Callaghan]] into [[minority government]] status, necessitating the [[Lib–Lab pact]].
*[[1967 Hamilton by-election]]: Scottish National Party victory massively boosted the prospects of the party.
*[[1966 Kingston upon Hull North by-election]]: Easy Labour victory in a marginal seat demonstrated to Prime Minister [[Harold Wilson]] that he would probably win a snap general election, and led to the construction of the [[Humber Bridge]].
*[[1965 Roxburgh, Selkirk and Peebles by-election]]: Rare Conservative loss in Opposition leads to resignation of leader Sir [[Alec Douglas-Home]] and election of [[Edward Heath]] as first democratically elected Conservative leader.
*[[1965 Leyton by-election]]: Foreign Secretary [[Patrick Gordon-Walker]], who was found the seat after losing [[Smethwick (UK Parliament constituency)|Smethwick]] in [[1964 United Kingdom general election|1964]], is again defeated; he is forced to resign from the Government.
*[[1963 Kinross and Western Perthshire by-election]]: Prime Minister Sir Alec Douglas-Home successfully returned to the House of Commons after disclaiming his peerage.
*[[1962 Orpington by-election]]: A Liberal gain in a suburban seat led to a national revival for the party.
*[[1961 Bristol South East by-election]]: Incumbent Labour MP [[Tony Benn]] re-elected after inheriting a peerage; the seat was awarded to the defeated Conservative, but the circumstances led to the [[Peerage Act 1963]] allowing hereditary peerages to be disclaimed.
*[[1938 Oxford by-election]]: After a campaign dominated by [[appeasement]] and the [[Munich agreement]], the government candidate won.
*[[1935 Liverpool Wavertree by-election]]: Intervention of Independent Conservative [[Randolph Churchill]], on platform of rearmament and anti-Indian Home Rule, hands safe seat to Labour on largest ever swing (30%). Indication of hostility to [[National Government (1931–1935)|National Government]], and Prime Minister [[Ramsay MacDonald]] resigns within months.
*[[1933 Fulham East by-election]]: Unexpected Labour gain in a previously safe Conservative constituency, ascribed to pacifism.
*[[1922 Newport by-election]]: Election of an anti-Coalition Conservative in a tight three-way contest spurred on Conservative MPs to end their coalition with [[David Lloyd George]].
*[[1920 Dartford by-election]]: massive swing to Labour prefigures the party's eclipse of the Liberals.

== Firsts and lasts ==
*Last [[Labour Party (UK)|Labour]] gain at a by-election [[2023 Mid Bedfordshire by-election]] and [[2023 Tamworth by-election]]
*Last [[Liberal Democrats (UK)|Liberal Democrat]] gain at a by-election: [[2023 Somerton and Frome by-election]]
*Last [[Conservative Party (UK)|Conservative]] gain in a by-election: [[2021 Hartlepool by-election]]
*First by-election to be called via the provisions of the [[Recall of MPs Act 2015]]: [[2019 Peterborough by-election]]
*First [[UK Independence Party]] gain at a by-election: [[2014 Clacton by-election]]
*Last [[UK Independence Party]] gain at a by-election: [[2014 Rochester and Strood by-election]] 
*First by-election gain by a Northern Ireland party: [[1943 Belfast West by-election]] ([[Northern Ireland Labour Party]] from [[Ulster Unionist Party]])
*Last by-election gain by a Northern Ireland party: [[2000 South Antrim by-election]] ([[Democratic Unionist Party]] from [[Ulster Unionist Party]])
*First by-election gain by the [[Social Democratic Party (UK)|Social Democratic Party]] (SDP): [[1981 Crosby by-election]]
*Last by-election gain by the [[Social Democratic Party (UK)|Social Democratic Party]] (SDP): [[1987 Greenwich by-election]]
*Last by-election gain by the [[Liberal Party (UK)|Liberal Party]]: [[1986 Ryedale by-election]]
*First by-election gain by the [[Scottish National Party]]: [[1945 Motherwell by-election]]
*Last by-election gain by the [[Scottish National Party]]: [[2008 Glasgow East by-election]]
*First and last by-election gain by [[Plaid Cymru]]: [[1966 Carmarthen by-election]]
*First by-election in which 18 year olds could vote, and party labels were included on the ballot: [[1970 Bridgwater by-election]]
*Last unopposed by-election in England, Scotland or Wales: [[1946 Hemsworth by-election]]
*Last by-election in a university constituency: [[1946 Combined Scottish Universities by-election]]
*Last by-election caused by appointment to ministerial office: [[1926 East Renfrewshire by-election]]
*Last by-election from what was to become the [[Irish Free State]]: [[1919 Dublin University by-election]]
*Last double member by-election: [[1920 Stockport by-election]]
*Last by-election result to be declared undue: [[1961 Bristol South East by-election]]
*Last by-election result to be declared void: [[1892 Cirencester by-election]]
*First by-election subject to the [[Corrupt and Illegal Practices Prevention Act 1883]]: [[1883 Limerick City by-election]]
*First by-election to be held using the [[secret ballot]]: [[1872 Pontefract by-election]]

==See also==
*[[List of United Kingdom by-elections]]
*[[United Kingdom European Parliament election records]]
*[[Swing (United Kingdom)]]
*[[Records of members of parliament of the United Kingdom]]
*[[United Kingdom general election records]]

==References==
((Reflist))

==Further reading==
* ''Who's Who of British MPs: Volume IV, 1945-1979'' by Michael Stenton and Stephen Lees (Harvester, Brighton, 1979) ((ISBN|0-85527-335-6))
* ''British Political Facts 1900-1994'' by David Butler and Gareth Butler (St. Martin's Press, New York, 1994) ((ISBN|0-312-12147-4))
* [http://www.parliament.uk/documents/commons/lib/research/rp2008/rp08-012.pdf ''Election Statistics 1918-2007''. House of Commons Library Research Paper 08/12]
((United Kingdom by-elections))

[[Category:Lists of by-elections to the Parliament of the United Kingdom]]
[[Category:Parliamentary records of the United Kingdom|By-election]]
[[Category:United Kingdom politics-related lists|By-election]]
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